shutdown

title: shutdown(8)

summary: bring the system down

text:
# shutdown(8)

## NAME
shutdown - bring the system down

## SYNOPSIS
/sbin/shutdown [-akrhPHfFnc] [-t sec] time [warning message]

## DESCRIPTION
shutdown brings the system down in a secure way. All logged-in users are notified that the system is going down, and login(1) is blocked. It is possible to shut the system down immediately or after a specified delay. All processes are first notified that the system is going down by the signal SIGTERM. This gives programs like vi(1) the time to save the file being edited, mail and news processing programs a chance to exit cleanly, etc. shutdown does its job by signalling the init process, asking it to change the runlevel. Runlevel 0 is used to halt the system, runlevel 6 is used to reboot the system, and runlevel 1 is used to put to system into a state where administrative tasks can be performed; this is the default if neither the -h or -r flag is given to shutdown. To see which actions are taken on halt or reboot see the appropriate entries for these runlevels in the file /etc/inittab.

## OPTIONS
-a

Use /etc/shutdown.allow.

-k

Don't really shutdown; only send the warning messages to everybody.

-r

Reboot after shutdown.

-h

Halt or power off after shutdown. Usually used with the -P or -H flags, depending on whether we want to poweroff or simply stop the operating system.

-P

Modifier to the -h flag. Halt action is to turn off the power. Must be used with the -h flag.

-H

Modifier to the -h flag. Halt action is to halt or drop into boot monitor on systems that support it. Must be used with the -h flag. Halting is often used to run through the shutdown process and leave output on the screen for debugging purposes. Or when the user wants the OS to stop, but leave the power on. To power off at the end of the shutdown sequence use the -P modifier instead.

-f

Skip fsck on reboot.

-F

Force fsck on reboot.

-n

[DEPRECATED] Don't call init(8) to do the shutdown but do it ourself. The use of this option is discouraged, and its results are not always what you'd expect.

-c

Cancel a waiting shutdown. ("shutdown now" is no longer waiting.) With this option it is of course not possible to give the time argument, but you can enter explanatory message arguments on the command line that will be sent to all users.

-q

Reduce the number of warnings shutdown displays. Usually shutdown displays warnings every 15 minutes and then every minute in the last 10 minutes of the countdown until time is reached. When -q is specified shutdown only warns at 60 minute intervals, at the 10 minute mark, at the 5 minue mark, and when the shutdown process actually happens.

-Q

Silence warnings prior to shutting down. Usually shutdown displays warnings every 15 minutes and then every minute in the last 10 minutes of the countdown until time is reached. When -Q is specified shutdown only warns when the shutdown process actually happens. All other warning intervals are suppressed.

-t sec

Tell init(8) to wait sec seconds between sending all processes the warning (SIGTERM) and the kill signal (SIGKILL), before changing to another runlevel. The default time, if no value is specified, between these two signals is three seconds. Warning: when shutdown calls init to perform the shutdown (the default behaviour), init checks to see if all processes have terminated and will stop waiting early once its children have all terminated. When shutdown is called with the -n flag, it waits the full time specified (or three seconds) even if all other processes have terminated.

time

When to shutdown.

warning message

Message to send to all users.

The time argument can have different formats. First, it can be an absolute time in the format hh:mm, in which hh is the hour (1 or 2 digits) and mm is the minute of the hour (in two digits). Second, it can be in the format +m, in which m is the number of minutes to wait. Third, it can be in the format +hh:mm, in which hh:mm is the number of hours and minutes to wait. The word now is an alias for +0.

If shutdown is called with a delay, it will create the advisory file /etc/nologin which causes programs such as login(1) to not allow new user logins. This file is created five minutes before the shutdown sequence starts. Shutdown removes this file if it is stopped before it can signal init (i.e. it is cancelled or something goes wrong). It also removes it before calling init to change the runlevel.

The -f flag means `reboot fast'. This only creates an advisory file /fastboot which can be tested by the system when it comes up again. The boot rc file can test if this file is present, and decide not to run fsck(1) since the system has been shut down in the proper way. After that, the boot process should remove /fastboot.

The -F flag means `force fsck'. This only creates an advisory file /forcefsck which can be tested by the system when it comes up again. The boot rc file can test if this file is present, and decide to run fsck(1) with a special `force' flag so that even properly unmounted file systems get checked. After that, the boot process should remove /forcefsck.

The -n flag causes shutdown not to call init, but to kill all running processes itself. shutdown will then turn off quota, accounting, and swapping and unmount all file systems.

## ACCESS CONTROL
shutdown can be called from init(8) when the magic keys CTRL-ALT-DEL are pressed, by creating an appropriate entry in /etc/inittab. This means that everyone who has physical access to the console keyboard can shut the system down. To prevent this, shutdown can check to see if an authorized user is logged in on one of the virtual consoles. If shutdown is called with the -a argument (add this to the invocation of shutdown in /etc/inittab), it checks to see if the file /etc/shutdown.allow is present. It then compares the login names in that file with the list of people that are logged in on a virtual console (from /var/run/utmp). Only if one of those authorized users or root is logged in, it will proceed. Otherwise it will write the message

```
shutdown: no authorized users logged in
```

to the (physical) system console. The format of /etc/shutdown.allow is one user name per line. Empty lines and comment lines (prefixed by a #) are allowed. Currently there is a limit of 32 users in this file.

Note that if /etc/shutdown.allow is not present, the -a argument is ignored.

## HALT OR POWEROFF
The -H option just sets the init environment variable INIT_HALT to HALT, and the -P option just sets that variable to POWEROFF. The script (usually /etc/init.d/halt) that calls the halt(8) program as the last thing in the shutting down sequence should check this environment variable and call the halt(8) program with the right options for these options to actually have any effect.

## FILES

```
/fastboot
/etc/inittab
/etc/init.d/halt
/etc/init.d/reboot
/etc/shutdown.allow
```

## NOTES
A lot of users forget to give the time argument and are then puzzled by the error message shutdown produces. The time argument is mandatory; in 90 percent of all cases this argument will be the word now.

Init can only capture CTRL-ALT-DEL and start shutdown in console mode. If the system is running the X window System, the X server processes all key strokes. Some X11 environments make it possible to capture CTRL-ALT-DEL, but what exactly is done with that event depends on that environment.

Shutdown wasn't designed to be run setuid. /etc/shutdown.allow is not used to find out who is executing shutdown, it ONLY checks who is currently logged in on (one of the) console(s).

## AUTHOR
Miquel van Smoorenburg, miquels@cistron.nl

## SEE ALSO
fsck(8), init(8), halt(8), poweroff(8), reboot(8)


bootlogd

package: sysvinit-utils

title: bootlogd(8)

summary: record boot messages

text:
# bootlogd(8)

## NAME
bootlogd - record boot messages

## SYNOPSIS
/sbin/bootlogd [-c] [-d] [-e] [-r] [-s] [-v] [ -l logfile ] [ -p pidfile ]

## DESCRIPTION
Bootlogd runs in the background and copies all strings sent to the /dev/console device to a logfile. If the logfile is not accessible, the messages will be kept in memory until it is.

## OPTIONS
-d

Do not fork and run in the background.

-e

Print escape characters to the boot log file. This turns off filtering of escape characters and allows tools like GNU Less to see and use colour control characters (show the log in colour).

-c

Attempt to write to the logfile even if it does not yet exist. Without this option, bootlogd will wait for the logfile to appear before attempting to write to it. This behavior prevents bootlogd from creating logfiles under mount points.

-r

If there is an existing logfile called logfile rename it to logfile~ unless logfile~ already exists.

-s

Ensure that the data is written to the file after each line by calling fdatasync(3). This will slow down a fsck(8) process running in parallel.

-v

Show version.

-l logfile

Log to this logfile. The default is /var/log/boot.

-p pidfile

Put process-id in this file. The default is no pidfile.

## NOTES
bootlogd saves log data which includes control characters. The log is technically a text file, but not very easy for humans to read. To address this the readbootlog(1) command can be used to display the boot log without the control characters.

## BUGS
Bootlogd works by redirecting the console output from the console device. (Consequently bootlogd requires PTY support in the kernel configuration.) It copies that output to the real console device and to a log file. There is no standard way of ascertaining the real console device if you have a new-style /dev/console device (major 5, minor 1) so bootlogd parses the kernel command line looking for console=... lines and deduces the real console device from that. If that syntax is ever changed by the kernel, or a console type is used that bootlogd does not know about then bootlogd will not work.

## AUTHOR
Miquel van Smoorenburg, miquels@cistron.nl

## SEE ALSO
dmesg(8),fdatasync(3),readbootlog(1).

branch: sisyphus


title: killall5(8)

text:
# killall5(8)

## NAME
killall5 -- send a signal to all processes.

## SYNOPSIS
killall5 -signalnumber [-o omitpid[,omitpid...]] [-o omitpid[,omitpid...]...]

## DESCRIPTION
killall5 is the SystemV killall command. It sends a signal to all processes except kernel threads and the processes in its own session, so it won't kill the shell that is running the script it was called from. Its primary (only) use is in the rc scripts found in the /etc/init.d directory.

## OPTIONS
-o omitpid

Tells killall5 to omit processes with that process id.

## NOTES
killall5 can also be invoked as pidof, which is simply a (symbolic) link to the killall5 program.

## EXIT STATUS
The program return zero if it killed processes. It return 2 if no process were killed, and 1 if it was unable to find any processes (/proc/ is missing).

## SEE ALSO
halt(8), reboot(8), pidof(8)

## AUTHOR
Miquel van Smoorenburg, miquels@cistron.nl


pidof

title: pidof(8)

text:
# pidof(8)

## NAME
pidof -- find the process ID of a running program.

## SYNOPSIS
pidof [-s] [-c] [-n] [-x] [-z] [-o omitpid[,omitpid...]] [-o omitpid[,omitpid...]...] [-d sep] program [program...]

## DESCRIPTION
Pidof finds the process id's (PIDs) of the named programs. It prints those id's on the standard output. This program is on some systems used in run-level change scripts, especially when the system has a System-V like rc structure. In that case these scripts are located in /etc/rc?.d, where ? is the runlevel. If the system has a start-stop-daemon (8) program that should be used instead.

## OPTIONS
-s

Single shot - this instructs the program to only return one pid.

-c

Only return process PIDs that are running with the same root directory. This option is ignored for non-root users, as they will be unable to check the current root directory of processes they do not own.

-n

Avoid stat(2) system function call on all binaries which are located on network based file systems like NFS. Instead of using this option the variable PIDOF_NETFS may be set and exported.

-q

Do not display matched PIDs to standard out. Simply exit with a status of true or false to indicate whether a matching PID was found.

-x

Scripts too - this causes the program to also return process id's of shells running the named scripts.

-z

Try to detect processes which are stuck in uninterruptible (D) or zombie (Z) status. Usually these processes are skipped as trying to deal with them can cause pidof to hang.

-d sep

Tells pidof to use sep as an output separator if more than one PID is shown. The default separator is a space.

-o omitpid

Tells pidof to omit processes with that process id. The special pid %PPID can be used to name the parent process of the pidof program, in other words the calling shell or shell script.

## EXIT STATUS
0

At least one program was found with the requested name.

1

No program was found with the requested name.

## NOTES
pidof is actually the same program as killall5; the program behaves according to the name under which it is called.

When pidof is invoked with a full pathname to the program it should find the pid of, it is reasonably safe. Otherwise it is possible that it returns PIDs of running programs that happen to have the same name as the program you're after but are actually other programs. Note that the executable name of running processes is calculated with readlink(2), so symbolic links to executables will also match.

Zombie processes or processes in disk sleep (states Z and D, respectively) are ignored, as attempts to access the stats of these will sometimes fail. The -z flag (see above) tells pidof to try to detect these sleeping and zombie processes, at the risk of failing or hanging.

## SEE ALSO
shutdown(8), init(8), halt(8), reboot(8), killall5(8)

## AUTHOR
Miquel van Smoorenburg, miquels@cistron.nl


title: t50(8)

text:
# t50(8)

## NAME
T50 - network packet injector

## SYNOPSIS
t50 [OPTION]... host[/CIDR]

## DESCRIPTION
Experimental mixed packet injector tool.

T50 must to be executed as root.

## OPTIONS
host[/CIDR]

The host address can be informed in one of two formats: IP address or URI name. In both cases the CIDR can be informed following the host name or IP using '/' as separator. Partial IP addresses can be informed. To do so, the user must exclude one or more octects (ex: 192.168 for 192.168.0.0/16 - "192.168." is an invalid host because of the last '.'). When using a partial IP address T50 will calculate CIDR automatically (8, 16 or 24 bits, if the first, second or thrid octect is informed, respectively).

--threshold NUM

Number of packets to send (default 1000).

--flood

Superseds the threshold.

-B, --bogus-csum

Bogus checksum.

--turbo

Extend performance (create child process).

-s, --saddr ADDR

IP source address (default RANDOM).

--help

Display full help.

## EXAMPLES
Send 500 packets to a single target:

\# t50 --threshold 500 192.168.0.100

Flood test:

$ t50 --flood 192.168.0.100

## AUTHORS
Nelson Brito

## CONTRIBUTORS
Fernando Mercês

Frederico Lamberti Pissarra

## REPORTING BUGS
Report t50 bugs at http://github.com/fredericopissarra/t50

## COPYRIGHT
Copyright © 2014 T50 developers. Licensed GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>. This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.


tacitus

package: tacitus

title: tacitus(8)

text:
# tacitus(8)

## NAME
tacitus - set sort-of-actual time on early boot of systems without RTC hardware (mostly embedded)

## SYNOPSIS
service tacitus [start|stop|restart|reload|status]

## OPTIONS
start - attempt to set previously saved time; the NTP daemon would (hopefully) do the rest

stop|restart|reload - save current time for future use

status - show current and (if file exists) saved time

## NAMED AFTER
Cornelius Tacitus - rerum gestarum scriptor Romanus.

## SEE ALSO
date(1)


targetctl

package: target-restore

title: targetctl(8)

text:
# targetctl(8)

## NAME
targetctl - Save and restore configuration of kernel target

## DESCRIPTION
targetctl is a low-level script to save and restore the configuration of the LIO kernel target, to and from a file in json format. It is not normally meant to be used by end-users directly, but by system init frameworks, or advanced end-users who are generating the configuration file themselves and need a way to load the configuration without relying on the targetcli configuration shell.

## USAGE
targetctl must be invoked as root. Exit status will be 0 if successful, or nonzero if an error was encountered.

targetctl save [config-file]

Saves the current configuration of the kernel target to a file in json format. Since the file may contain cleartext passwords, the file's permissions will be set to only allow root access. If config-file is not supplied, targetctl will use the default file location, /etc/target/saveconfig.json.

targetctl restore [config-file]

Removes any existing configuration and replaces it with the configuration described in the file. See saveconfig.json(5) for more details. If parts of the configuration could not be restored, those parts will be noted in the error output, and the rest of the configuration will still be applied.

targetctl clear

Removes any existing configuration from the running kernel target.

targetctl --help

Displays usage information.

## SEE ALSO
targetcli(8), targetd(8), saveconfig.json(5)

## FILES
/etc/target/saveconfig.json

/sys/kernel/config/target

## AUTHOR
Written by Andy Grover <agrover@redhat.com>.

Man page written by Andy Grover <agrover@redhat.com>.

## REPORTING BUGS
Report bugs via <targetcli-fb-devel@lists.fedorahosted.org>

or <https://github.com/open-iscsi/rtslib-fb/issues>


targetcli

package: targetcli

title: targetcli(8)

text:
# targetcli(8)

## NAME
targetcli - administration shell for storage targets

## DESCRIPTION
targetcli is a shell for viewing, editing, and saving the configuration of the kernel's target subsystem, also known as LIO. It enables the administrator to assign local storage resources backed by either files, volumes, local SCSI devices, or ramdisk, and export them to remote systems via network fabrics, such as iSCSI or FCoE.

There is a daemon component for targetcli, which will greatly improve the overall execution time taken by targetcli commands at scale. For more details about switching to daemonized mode refer to targetclid(8) man page.

The configuration layout is tree-based, similar to a filesystem, and is navigated in a similar manner.

## USAGE
targetcli

targetcli [cmd]

Invoke targetcli as root to enter the configuration shell, or follow with a command to execute but do not enter the shell. Use ls to list nodes below the current path. Moving around the tree is accomplished by the cd command, or by entering the new location directly. Objects are created using create, removed using delete. Use help <cmd> for additional usage information. Tab-completion is available for commands and command arguments.

Configuration changes in targetcli are made immediately to the underlying kernel target configuration. Settings will not be retained across reboot unless saveconfig is either explicitly called, or implicitly by exiting the shell with the global preference auto_save_on_exit set to true, the default.

## QUICKSTART
To create an iSCSI target and share a file-backed LUN without any auth checks:

$ sudo targetcli

/> backstores/fileio create test /tmp/test.img 100m

/> iscsi/ create iqn.2006-04.com.example:test-target

/> cd iscsi/iqn.2006-04.com.example:test-target/tpg1/

tpg1/> luns/ create /backstores/fileio/test

tpg1/> set attribute generate_node_acls=1

tpg1/> exit

Although by default targetcli saves the running configuration upon exit, a distribution-specific service must be enabled to restore the saved configuration on reboot. See distribution documentation for specifics, but for example:

$ sudo systemctl enable target.service

See EXAMPLES below for more detailed information on commands and using the shell.

## BACKSTORES
Backstores are different kinds of local storage resources that the kernel target uses to "back" the SCSI devices it exports. The mappings to local storage resources that each backstore creates are called storage objects.

### FILEIO
Allows files to be treated as disk images. When storage objects of this type are created, they can support either write-back or write-thru operation. Using write-back enables the local filesystem cache, which will improve performance but increase the risk of data loss. It is also possible to use fileio with local block device files, if buffered operation is needed.

Fileio also supports using an existing file, or creating a new file. New files are sparsely allocated by default.

### BLOCK
Allows a local disk block device to be shared.

### PSCSI
Allows a local SCSI device of any type to be shared. It is generally advised to prefer the block backstore if sharing a block SCSI device is desired.

### RAMDISK
Allows kernel memory to be shared as a block SCSI device. Since memory is volatile, the contents of the ramdisk will be lost if the system restarts, and this backstore is best used for testing only.

It also supports "nullio" mode, which is not backed by any storage. It discards all writes, and returns all-zeroes for reads.

### USERSPACE-BACKED
Backstores starting with "user:" are not supported in the kernel, but rely on a userspace process to handle requests. See tcmu-runner(8) for more information on creating backstores of this type.

## TARGETS
Targets are instances of a fabric, which adapts the kernel target to a specific transport protocol such as iSCSI, Fibre Channel, or SBP-2. Creating a target in targetcli enables that target to be configured. The name of the target, its WWN (world wide name), may link the configuration to a specific hardware endpoint, like SRP for example, or it may not, like iSCSI.

Aside from "backstores", all other top-level configuration nodes in targetcli are fabrics that may have targets created for them. Fabrics that require hardware are only listed if the hardware is present and configured properly.

### CREATING A TARGET
Use the create command within a fabric's node to create a target. If the fabric's targets are tied to hardware then targetcli will constrain the WWN to available hardware WWNs. These can be shown via tab-completion. If the fabric is not tied to hardware, such as iSCSI, then targetcli will either auto-generate a WWN if none is given, or check that the given WWN has the correct format. All WWNs are prefaced by their type, such as "iqn", "naa", or "ib", and may be given with or without colons.

iSCSI supports multiple WWN formats: iqn, naa, and eui. Other fabrics support single formats only.

## CONFIGURING A TARGET
Not all fabrics have the same capabilities. Targets on different fabrics will have different configuration node layouts. iSCSI has the most to configure; other fabrics present subsets of iSCSI's feature set.

## CONFIGURING ISCSI
iSCSI has the most options for configuration.

### TPGS
TPGs (Target Portal Groups) allow the iSCSI to support multiple complete configurations within one target. This is useful for complex quality-of-service configurations. targetcli will automatically create one TPG when the target is created, and almost all setups only need one.

### PORTALS
An iSCSI target may be reached via multiple IP addresses and ports. These addr:port pairs are called portals. Both IPv4 and IPv6 addresses are supported.

When a target is created, targetcli automatically creates a default portal listening on all IPv4 and IPv6 addresses (shown as ::0) on port 3260. If IPV6_V6ONLY is set, the default will only listen on all IPv6 addresses. If a different configuration is needed, the default portal can be removed and portals configured as desired.

If the hardware supports it, iSER (iSCSI Extensions for RDMA) may be enabled via the enable_iser command within each portal's node. Or, if the hardware supports it, hardware offload may be enabled via the enable_offload command within each portal's node.

### LUNS
The kernel target exports SCSI Logical Units, also called LUNs. This section links the previously-defined storage objects with the target, and defines which number (the Logical Unit Number) the device will use. Note that if ACLs are being used, a lun mapping must be created under the ACL that refers back to the TPG LUN.

### ACLS
ACLs (Access Control Lists) allow different configuration, depending on the initiator that is connecting to the target. This includes both per-initiator authentication settings as well as per-initiator LUN mappings.

create <wwn> in the acls node creates an ACL for an initiator, and create within the ACL creates a LUN mapping. (This can either refer to the TPG LUN, or to the storage object, in which case the TPG LUN will be configured as well.) Global setting auto_add_mapped_luns affects this, see below.

### AUTHENTICATION
iSCSI supports authentication via the CHAP protocol, which uses a username and password. The initiator may be required to supply valid credentials to the target, and the target may also be required to supply credentials back to the initiator. The latter is referred to as mutual authentication.

Furthermore, authentication credentials may be different for each session phase (Discovery or Normal), and authentication in a Normal session may be set at the TPG level, or per-ACL.

Discovery Authentication

iSCSI Discovery sessions allow the initiator to connect to a portal and discover targets with the SendTargets command, but not access them. The four parameters userid, password, mutual_userid, and mutual_password are configured via set discovery_auth command within the top-level iscsi configuration node. 1-way authentication is enabled if userid and password are both set, and mutual authentication is enabled if all four are set. Authentication is disabled by unsetting the parameters.

Normal Authentication

Similarly, the four parameters userid, password, mutual_userid, and mutual_password are configured via set auth command within the TPG node and ACL nodes. However, LIO only uses one or the other, depending on the TPG's generate_node_acls attribute setting. If generate_node_acls is 1, the TPG-wide settings will be used. If generate_node_acls is 0, then the user-created ACLs' settings will be used.

Enable generate_node_acls with set attribute generate_node_acls=1 within the TPG node. This can be thought of as "ignore ACLs mode" -- both authentication and LUN mapping will then use the TPG settings.

No Authentication

Authentication is disabled by clearing the TPG "authentication" attribute: set attribute authentication=0. Although initiator names are trivially forgeable, generate_node_acls still works here to either ignore user-defined ACLs and allow all, or check that an ACL exists for the connecting initiator.

## CONFIGURING FIBRE CHANNEL (QLA2XXX)
Operation as a target requires that /sys/module/qla2xxx/parameters/qlini_mode report "disabled". This may require passing the qlini_mode=disabled parameter to the qla2xxx module when it loads.

## CONFIGURING FIBRE CHANNEL OVER ETHERNET (TCM_FC)
Ensure fcoeadm -i shows a working endpoint.

## CONFIGURING SRP
SRP (SCSI RDMA Protocol) requires that RDMA-capable hardware is present. It uses "ib" WWNs.

## CONFIGURING LOOPBACK
Storage objects may be re-exported as local SCSI devices with this fabric.

## CONFIGURING OTHER FABRICS
Other fabrics may be present. They are for specialized uses. Use at your own risk.

## EXAMPLES

### DEFINING A STORAGE OBJECT WITHIN A BACKSTORE
backstores/fileio create disk1 /disks/disk1.img 140M

Creates a storage object named disk1 with the given path and size. targetcli supports common size abbreviations like 'M', 'G', and 'T'.

### EXPORTING A STORAGE OBJECT VIA ISCSI
iscsi/ create

Creates an iSCSI target with a default WWN. It will also create an initial target portal group called tpg1.

iqn.2003-01.org.linux-iscsi.test2.x8664:sn123456789012/tpg1/

An example of changing to the configuration node for the given target's first target portal group (TPG). This is equivalent to giving the command prefixed by "cd". (Although more can be useful for certain setups, most configurations have a single TPG per target. In this case, configuring the TPG is equivalent to configuring the overall target.)

portals/ create

Add a portal, i.e. an IP address and TCP port via which the target can be contacted by initiators. Only required if the default [::0]:3260 portal is not present.

luns/ create /backstores/fileio/disk1

Create a new LUN in the TPG, attached to the storage object that has previously been defined. The storage object now shows up under the /backstores configuration node as activated.

acls/ create iqn.1994-05.com.redhat:4321576890

Creates an ACL (access control list) entry for the given iSCSI initiator.

acls/iqn.1994-05.com.redhat:4321576890 create 2 0

Gives the initiator access to the first exported LUN (lun0), which the initiator will see as lun2. The default is to give the initiator read/write access; if read-only access was desired, an additional "1" argument would be added to enable write-protect. (Note: if global setting auto_add_mapped_luns is true, this step is not necessary.)

### EXPORTING A STORAGE OBJECT VIA FCOE
tcm_fc/ create 20:00:00:19:99:a8:34:bc

Create an FCoE target with the given WWN. targetcli can tab-complete the WWN based on registered FCoE interfaces. If none are found, verify that they are properly configured and are shown in the output of fcoeadm -i.

tcm_fc/20:00:00:19:99:a8:34:bc/

If auto_cd_after_create is set to false, change to the configuration node for the given target, equivalent to giving the command prefixed by cd.

luns/ create /backstores/fileio/disk1

Create a new LUN for the interface, attached to a previously defined storage object. The storage object now shows up under the /backstores configuration node as activated.

acls/ create 00:99:88:77:66:55:44:33

Create an ACL (access control list), for defining the resources each initiator may access. The default behavior is to auto-map existing LUNs to the ACL; see help for more information.

The LUN should now be accessible via FCoE.

## OTHER COMMANDS
saveconfig

Save the current configuration settings to a file, from which settings will be restored if the system is rebooted. By default, this will save the configuration to /etc/target/saveconfig.json.

This command is executed from the configuration root node.

restoreconfig

Restore target configuration from a file, the default is the file listed under saveconfig. This will fail if there is already an established config, unless the clear_existing option is set to true.

This command is executed from the configuration root node.

clearconfig

Clears the entire current local configuration. The parameter confirm=true must also be given, as a precaution.

This command is executed from the configuration root node.

sessions [ list | detail ] [sid]

Lists the current open sessions or a specific session, with or without details.

This command is executed from the configuration root node.

exit

Leave the configuration shell.

## SETTINGS GROUPS
Settings are broken into groups. Individual settings are accessed by get <group> <setting> and set <group> <setting>=<value>, and the settings of an entire group may be displayed by get <group>. All except for global are associated with a particular configuration node.

### GLOBAL
Shell-related user-specific settings are in global, and are visible from all configuration nodes. They are mostly shell display options, but some starting with auto_ affect shell behavior and may merit customization. These include auto_save_on_exit, which controls if exiting targetcli saves the configuration; auto_add_mapped_luns, to automatically add existing LUNs to new ACLs, and new LUNS to existing ACLs; and auto_cd_after_create, to change working path to newly-created nodes. Global settings are user-specific and are saved to ~/.targetcli/ upon exit, unlike other groups, which are system-wide and kept in /etc/target/saveconfig.json.

### BACKSTORE-SPECIFIC
attribute

/backstore/<type>/<name> configuration node. Contains values relating to the backstore and storage object.

### ISCSI-SPECIFIC
discovery_auth

/iscsi configuration node. Set the normal and mutual authentication userid and password for discovery sessions, as well as enabling or disabling it. By default it is disabled -- no authentication is required for discovery.

parameter

/iscsi/<target_iqn>/tpgX configuration node. ISCSI-specific parameters such as AuthMethod, MaxBurstLength, IFMarker, DataDigest, and similar.

attribute

/iscsi/<target_iqn>/tpgX configuration node. Contains implementation-specific settings for the TPG, such as authentication, to enforce or disable authentication for the full-feature phase (i.e. non-discovery).

auth

/iscsi/<target_iqn>/tpgX/acls/<initiator_iqn> configuration node. Set the userid and password for full-feature phase for this ACL.

## FILES
/etc/target/saveconfig.json

/etc/target/backup/*

## ENVIRONMENT

### TARGETCLI_HOME
If set, this variable points to a directory that should be used instead of ~/.targetcli

## SEE ALSO
targetclid(8), targetctl(8), tcmu-runner(8)

## AUTHOR
Written by Jerome Martin <jxm@risingtidesystems.com>.

Man page written by Andy Grover <agrover@redhat.com>.

## REPORTING BUGS
Report bugs via <targetcli-fb-devel@lists.fedorahosted.org>

or <https://github.com/open-iscsi/targetcli-fb/issues>


tayga

package: tayga

title: tayga(8)

summary: stateless NAT64 daemon

text:
# tayga(8)

## NAME
tayga - stateless NAT64 daemon

## SYNOPSIS
tayga [OPTION]...

tayga --mktun [OPTION]...

tayga --rmtun [OPTION]...

## DESCRIPTION
TAYGA is a stateless NAT64 daemon for Linux. Using the in-kernel TUN network driver, TAYGA receives IPv4 and IPv6 packets from the host's network stack, translates them to the other protocol, and then sends the translated packets back to the host using the same TUN interface.

Translation is compliant with IETF Internet-Draft draft-ietf-behave-v6v4-xlate-23, and address mapping is performed in accordance with RFC 6052. Optionally, TAYGA may be configured to dynamically map IPv6 hosts to addresses drawn from a configured IPv4 address pool.

As a stateless NAT, TAYGA requires a one-to-one mapping between IPv4 addresses and IPv6 addresses. Mapping multiple IPv6 addresses onto a single IPv4 address can be achieved by mapping IPv6 addresses to private IPv4 addresses with TAYGA and then using a stateful NAT44 (such as the iptables(8) MASQUERADE target) to map the private IPv4 addresses onto the desired single IPv4 address.

TAYGA's configuration is stored in the tayga.conf(5) file, which is usually found in /etc/tayga.conf or /usr/local/etc/tayga.conf.

## INVOCATION
Without the --mktun or --rmtun options, the `tayga` executable runs as a daemon, translating packets as described above.

The --mktun and --rmtun options instruct TAYGA to create or destroy, respectively, its configured TUN device as a "persistent" interface and then immediately exit.

Persistent TUN devices remain present on the host system even when TAYGA is not running. This allows host-side network parameters and firewall rules to be configured prior to commencement of packet translation. This may simplify network configuration on the host; for example, systems which use a Debian-style /etc/network/interfaces file may configure TAYGA's TUN device at boot by running `tayga --mktun` as a "pre-up" command and then configuring the TUN device as any other network interface.

## OPTIONS
-c configfile | --config configfile

Read configuration options from configfile

-d

Enable debug messages (enables --nodetach as well)

-n | --nodetach

Do not detach from terminal

-u userid | --user userid

Set uid to userid after initialization

-g groupid | --group groupid

Set gid to groupid after initialization

-r | --chroot

chroot() to data-dir (specified in config file)

-p pidfile | --pidfile pidfile

Write process ID of daemon to pidfile

## AUTHOR
Written by Nathan Lutchansky <lutchann@litech.org>

## COPYRIGHT
Copyright © 2010 Nathan Lutchansky

License GPLv2+: GNU GPL version 2 or later

This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.

## SEE ALSO
tayga.conf(5)

<http://www.litech.org/tayga/>


package: tcb-utils

title: tcb_convert(8)

summary: utilities to convert to and from

text:
# tcb_convert(8)

## NAME
tcb_convert, tcb_unconvert - utilities to convert to and from the tcb password shadowing scheme

## SYNOPSIS
tcb_convert

tcb_unconvert

## DESCRIPTION
tcb_convert converts /etc/shadow into a set of files under /etc/tcb/ (see tcb(5)). During this operation /etc/shadow is locked.

tcb_unconvert converts the files under /etc/tcb/ back into /etc/shadow. Because it is impractical to lock all of the tcb shadow files, tcb_unconvert temporarily changes the group ownership on /etc/tcb/ to group "sys" such that the passwd(1) utility will refuse to work during the conversion.

## MIGRATING TO TCB
In order to migrate a system to the tcb password shadowing scheme from the traditional /etc/passwd+/etc/shadow setup, the following steps are necessary:

1.

Install the tcb package as well as tcb-aware shadow-utils.

2.

Create the group "auth" if it isn't present.

3.

If you want processes possessing both "shadow" and "auth" groups to have read-only access to all tcb files, add or uncomment the following line in /etc/login.defs: TCB_AUTH_GROUP yes

4.

As root, execute tcb_convert.

5.

In /etc/nsswitch.conf, find the "shadow" entry and replace the "files" method with "tcb"; the edited line should look like this: shadow: tcb

6.

In /etc/pam.d/ files, change occurrences of pam_unix.so or pam_pwdb.so (if any) to pam_tcb.so. You may wish to browse the pam_tcb(8) manual for information on additional tuning.

7.

In each file under /etc/pam.d/ which has a "password" line (most notably in /etc/pam.d/passwd) add the write_to=tcb option to the instance of pam_tcb used as the password changing module. The line should look similar to this: password required /lib/security/pam_tcb.so shadow use_authtok write_to=tcb

8.

Edit /etc/login.defs such that it contains the (uncommented) line: USE_TCB yes

9.

Now you should remove the /etc/shadow file and its backups (if any), such as /etc/shadow-. It is important that you do so such that processes possessing the "shadow" group don't get read access to all of your old password hashes (many of which may remain valid for quite some time).

10.

As root, chown root:shadow /usr/bin/passwd /etc/pam.d/passwd

chmod 2711 /usr/bin/passwd

chmod 640 /etc/pam.d/passwd

11.

Test if everything works properly, most notably logging in to the system.

## THE RETURN TO SHADOW
If for some reason you decide to return from tcb to the traditional password shadowing scheme, you can do so with the use of tcb_unconvert and by reverting some of the actions listed in "MIGRATING TO TCB", above.

## SEE ALSO
login.defs(5), tcb(5), pam_tcb(8)


tcpdump

package: tcpdump

title: tcpdump(8)

summary: dump traffic on a network

text:
# tcpdump(8)

## NAME
tcpdump - dump traffic on a network

## SYNOPSIS
tcpdump [ -AbdDefhHIJKlLnNOpqStuUvxX# ] [ -B buffer_size ] [ -c count ] [ --count ] [ -C file_size ] [ -E spi@ipaddr algo:secret,... ] [ -F file ] [ -G rotate_seconds ] [ -i interface ] [ --immediate-mode ] [ -j tstamp_type ] [ -m module ] [ -M secret ] [ --number ] [ --print ] [ -Q in|out|inout ] [ -r file ] [ -s snaplen ] [ -T type ] [ --version ] [ -V file ] [ -w file ] [ -W filecount ] [ -y datalinktype ] [ -z postrotate-command ] [ -Z user ] [ --time-stamp-precision=tstamp_precision ] [ --micro ] [ --nano ] [ expression ]

## DESCRIPTION
Tcpdump prints out a description of the contents of packets on a network interface that match the Boolean expression (see pcap-filter(7) for the expression syntax); the description is preceded by a time stamp, printed, by default, as hours, minutes, seconds, and fractions of a second since midnight. It can also be run with the -w flag, which causes it to save the packet data to a file for later analysis, and/or with the -r flag, which causes it to read from a saved packet file rather than to read packets from a network interface. It can also be run with the -V flag, which causes it to read a list of saved packet files. In all cases, only packets that match expression will be processed by tcpdump.

Tcpdump will, if not run with the -c flag, continue capturing packets until it is interrupted by a SIGINT signal (generated, for example, by typing your interrupt character, typically control-C) or a SIGTERM signal (typically generated with the kill(1) command); if run with the -c flag, it will capture packets until it is interrupted by a SIGINT or SIGTERM signal or the specified number of packets have been processed.

When tcpdump finishes capturing packets, it will report counts of:

packets ``captured'' (this is the number of packets that tcpdump has received and processed);

packets ``received by filter'' (the meaning of this depends on the OS on which you're running tcpdump, and possibly on the way the OS was configured - if a filter was specified on the command line, on some OSes it counts packets regardless of whether they were matched by the filter expression and, even if they were matched by the filter expression, regardless of whether tcpdump has read and processed them yet, on other OSes it counts only packets that were matched by the filter expression regardless of whether tcpdump has read and processed them yet, and on other OSes it counts only packets that were matched by the filter expression and were processed by tcpdump);

packets ``dropped by kernel'' (this is the number of packets that were dropped, due to a lack of buffer space, by the packet capture mechanism in the OS on which tcpdump is running, if the OS reports that information to applications; if not, it will be reported as 0).

On platforms that support the SIGINFO signal, such as most BSDs (including macOS) and Digital/Tru64 UNIX, it will report those counts when it receives a SIGINFO signal (generated, for example, by typing your ``status'' character, typically control-T, although on some platforms, such as macOS, the ``status'' character is not set by default, so you must set it with stty(1) in order to use it) and will continue capturing packets. On platforms that do not support the SIGINFO signal, the same can be achieved by using the SIGUSR1 signal.

Using the SIGUSR2 signal along with the -w flag will forcibly flush the packet buffer into the output file.

Reading packets from a network interface may require that you have special privileges; see the pcap(3PCAP) man page for details. Reading a saved packet file doesn't require special privileges.

## OPTIONS
-A

Print each packet (minus its link level header) in ASCII. Handy for capturing web pages.

-b

Print the AS number in BGP packets in ASDOT notation rather than ASPLAIN notation.

-B buffer_size

--buffer-size=buffer_size

Set the operating system capture buffer size to buffer_size, in units of KiB (1024 bytes).

-c count

Exit after receiving count packets.

--count

Print only on stdout the packet count when reading capture file(s) instead of parsing/printing the packets. If a filter is specified on the command line, tcpdump counts only packets that were matched by the filter expression.

-C file_size

Before writing a raw packet to a savefile, check whether the file is currently larger than file_size and, if so, close the current savefile and open a new one. Savefiles after the first savefile will have the name specified with the -w flag, with a number after it, starting at 1 and continuing upward. The units of file_size are millions of bytes (1,000,000 bytes, not 1,048,576 bytes). ALT-specific note: when used with -Z option (enabled by default), privileges are dropped before opening first savefile.

-d

Dump the compiled packet-matching code in a human readable form to standard output and stop.

Please mind that although code compilation is always DLT-specific, typically it is impossible (and unnecessary) to specify which DLT to use for the dump because tcpdump uses either the DLT of the input pcap file specified with -r, or the default DLT of the network interface specified with -i, or the particular DLT of the network interface specified with -y and -i respectively. In these cases the dump shows the same exact code that would filter the input file or the network interface without -d.

However, when neither -r nor -i is specified, specifying -d prevents tcpdump from guessing a suitable network interface (see -i). In this case the DLT defaults to EN10MB and can be set to another valid value manually with -y.

-dd

Dump packet-matching code as a C program fragment.

-ddd

Dump packet-matching code as decimal numbers (preceded with a count).

-D

--list-interfaces

Print the list of the network interfaces available on the system and on which tcpdump can capture packets. For each network interface, a number and an interface name, possibly followed by a text description of the interface, are printed. The interface name or the number can be supplied to the -i flag to specify an interface on which to capture.

This can be useful on systems that don't have a command to list them (e.g., Windows systems, or UNIX systems lacking ifconfig -a); the number can be useful on Windows 2000 and later systems, where the interface name is a somewhat complex string.

The -D flag will not be supported if tcpdump was built with an older version of libpcap that lacks the pcap_findalldevs(3PCAP) function.

-e

Print the link-level header on each dump line. This can be used, for example, to print MAC layer addresses for protocols such as Ethernet and IEEE 802.11.

-E

Use spi@ipaddr algo:secret for decrypting IPsec ESP packets that are addressed to addr and contain Security Parameter Index value spi. This combination may be repeated with comma or newline separation.

Note that setting the secret for IPv4 ESP packets is supported at this time.

Algorithms may be des-cbc, 3des-cbc, blowfish-cbc, rc3-cbc, cast128-cbc, or none. The default is des-cbc. The ability to decrypt packets is only present if tcpdump was compiled with cryptography enabled.

secret is the ASCII text for ESP secret key. If preceded by 0x, then a hex value will be read.

The option assumes RFC 2406 ESP, not RFC 1827 ESP. The option is only for debugging purposes, and the use of this option with a true `secret' key is discouraged. By presenting IPsec secret key onto command line you make it visible to others, via ps(1) and other occasions.

In addition to the above syntax, the syntax file name may be used to have tcpdump read the provided file in. The file is opened upon receiving the first ESP packet, so any special permissions that tcpdump may have been given should already have been given up.

-f

Print `foreign' IPv4 addresses numerically rather than symbolically (this option is intended to get around serious brain damage in Sun's NIS server — usually it hangs forever translating non-local internet numbers).

The test for `foreign' IPv4 addresses is done using the IPv4 address and netmask of the interface on that capture is being done. If that address or netmask are not available, either because the interface on that capture is being done has no address or netmask or because it is the "any" pseudo-interface, which is available in Linux and in recent versions of macOS and Solaris, and which can capture on more than one interface, this option will not work correctly.

-F file

Use file as input for the filter expression. An additional expression given on the command line is ignored.

-G rotate_seconds

If specified, rotates the dump file specified with the -w option every rotate_seconds seconds. Savefiles will have the name specified by -w which should include a time format as defined by strftime(3). If no time format is specified, each new file will overwrite the previous. Whenever a generated filename is not unique, tcpdump will overwrite the preexisting data; providing a time specification that is coarser than the capture period is therefore not advised.

If used in conjunction with the -C option, filenames will take the form of `file<count>'. ALT-specific note: when used with -Z option (enabled by default), privileges are dropped before opening first savefile.

-h

--help

Print the tcpdump and libpcap version strings, print a usage message, and exit.

--version

Print the tcpdump and libpcap version strings and exit.

-H

Attempt to detect 802.11s draft mesh headers.

-i interface

--interface=interface

Listen, report the list of link-layer types, report the list of time stamp types, or report the results of compiling a filter expression on interface. If unspecified and if the -d flag is not given, tcpdump searches the system interface list for the lowest numbered, configured up interface (excluding loopback), which may turn out to be, for example, ``eth0''.

On Linux systems with 2.2 or later kernels and on recent versions of macOS and Solaris, an interface argument of ``any'' can be used to capture packets from all interfaces. Note that captures on the ``any'' pseudo-interface will not be done in promiscuous mode.

If the -D flag is supported, an interface number as printed by that flag can be used as the interface argument, if no interface on the system has that number as a name.

-I

--monitor-mode

Put the interface in "monitor mode"; this is supported only on IEEE 802.11 Wi-Fi interfaces, and supported only on some operating systems.

Note that in monitor mode the adapter might disassociate from the network with which it's associated, so that you will not be able to use any wireless networks with that adapter. This could prevent accessing files on a network server, or resolving host names or network addresses, if you are capturing in monitor mode and are not connected to another network with another adapter.

This flag will affect the output of the -L flag. If -I isn't specified, only those link-layer types available when not in monitor mode will be shown; if -I is specified, only those link-layer types available when in monitor mode will be shown.

--immediate-mode

Capture in "immediate mode". In this mode, packets are delivered to tcpdump as soon as they arrive, rather than being buffered for efficiency. This is the default when printing packets rather than saving packets to a ``savefile'' if the packets are being printed to a terminal rather than to a file or pipe.

-j tstamp_type

--time-stamp-type=tstamp_type

Set the time stamp type for the capture to tstamp_type. The names to use for the time stamp types are given in pcap-tstamp(7); not all the types listed there will necessarily be valid for any given interface.

-J

--list-time-stamp-types

List the supported time stamp types for the interface and exit. If the time stamp type cannot be set for the interface, no time stamp types are listed.

--time-stamp-precision=tstamp_precision

When capturing, set the time stamp precision for the capture to tstamp_precision. Note that availability of high precision time stamps (nanoseconds) and their actual accuracy is platform and hardware dependent. Also note that when writing captures made with nanosecond accuracy to a savefile, the time stamps are written with nanosecond resolution, and the file is written with a different magic number, to indicate that the time stamps are in seconds and nanoseconds; not all programs that read pcap savefiles will be able to read those captures.

When reading a savefile, convert time stamps to the precision specified by timestamp_precision, and display them with that resolution. If the precision specified is less than the precision of time stamps in the file, the conversion will lose precision.

The supported values for timestamp_precision are micro for microsecond resolution and nano for nanosecond resolution. The default is microsecond resolution.

--micro

--nano

Shorthands for --time-stamp-precision=micro or --time-stamp-precision=nano, adjusting the time stamp precision accordingly. When reading packets from a savefile, using --micro truncates time stamps if the savefile was created with nanosecond precision. In contrast, a savefile created with microsecond precision will have trailing zeroes added to the time stamp when --nano is used.

-K

--dont-verify-checksums

Don't attempt to verify IP, TCP, or UDP checksums. This is useful for interfaces that perform some or all of those checksum calculation in hardware; otherwise, all outgoing TCP checksums will be flagged as bad.

-l

Make stdout line buffered. Useful if you want to see the data while capturing it. E.g.,

```
tcpdump -l | tee dat
```

or

```
tcpdump -l > dat & tail -f dat
```

Note that on Windows,``line buffered'' means ``unbuffered'', so that WinDump will write each character individually if -l is specified.

-U is similar to -l in its behavior, but it will cause output to be ``packet-buffered'', so that the output is written to stdout at the end of each packet rather than at the end of each line; this is buffered on all platforms, including Windows.

-L

--list-data-link-types

List the known data link types for the interface, in the specified mode, and exit. The list of known data link types may be dependent on the specified mode; for example, on some platforms, a Wi-Fi interface might support one set of data link types when not in monitor mode (for example, it might support only fake Ethernet headers, or might support 802.11 headers but not support 802.11 headers with radio information) and another set of data link types when in monitor mode (for example, it might support 802.11 headers, or 802.11 headers with radio information, only in monitor mode).

-m module

Load SMI MIB module definitions from file module. This option can be used several times to load several MIB modules into tcpdump.

-M secret

Use secret as a shared secret for validating the digests found in TCP segments with the TCP-MD5 option (RFC 2385), if present.

-n

Don't convert host addresses to names. This can be used to avoid DNS lookups.

-nn

Don't convert protocol and port numbers etc. to names either.

-N

Don't print domain name qualification of host names. E.g., if you give this flag then tcpdump will print ``nic'' instead of ``nic.ddn.mil''.

-#

--number

Print a packet number at the beginning of the line.

-O

--no-optimize

Do not run the packet-matching code optimizer. This is useful only if you suspect a bug in the optimizer.

-p

--no-promiscuous-mode

Don't put the interface into promiscuous mode. Note that the interface might be in promiscuous mode for some other reason; hence, `-p' cannot be used as an abbreviation for `ether host {local-hw-addr} or ether broadcast'.

--print

Print parsed packet output, even if the raw packets are being saved to a file with the -w flag.

-Q direction

--direction=direction

Choose send/receive direction direction for which packets should be captured. Possible values are `in', `out' and `inout'. Not available on all platforms.

-q

Quick (quiet?) output. Print less protocol information so output lines are shorter.

-r file

Read packets from file (which was created with the -w option or by other tools that write pcap or pcapng files). Standard input is used if file is ``-''.

-S

--absolute-tcp-sequence-numbers

Print absolute, rather than relative, TCP sequence numbers.

-s snaplen

--snapshot-length=snaplen

Snarf snaplen bytes of data from each packet rather than the default of 262144 bytes. Packets truncated because of a limited snapshot are indicated in the output with ``[|proto]'', where proto is the name of the protocol level at which the truncation has occurred.

Note that taking larger snapshots both increases the amount of time it takes to process packets and, effectively, decreases the amount of packet buffering. This may cause packets to be lost. Note also that taking smaller snapshots will discard data from protocols above the transport layer, which loses information that may be important. NFS and AFS requests and replies, for example, are very large, and much of the detail won't be available if a too-short snapshot length is selected.

If you need to reduce the snapshot size below the default, you should limit snaplen to the smallest number that will capture the protocol information you're interested in. Setting snaplen to 0 sets it to the default of 262144, for backwards compatibility with recent older versions of tcpdump.

-T type

Force packets selected by "expression" to be interpreted the specified type. Currently known types are aodv (Ad-hoc On-demand Distance Vector protocol), carp (Common Address Redundancy Protocol), cnfp (Cisco NetFlow protocol), domain (Domain Name System), lmp (Link Management Protocol), pgm (Pragmatic General Multicast), pgm_zmtp1 (ZMTP/1.0 inside PGM/EPGM), ptp (Precision Time Protocol), radius (RADIUS), resp (REdis Serialization Protocol), rpc (Remote Procedure Call), rtcp (Real-Time Applications control protocol), rtp (Real-Time Applications protocol), snmp (Simple Network Management Protocol), someip (SOME/IP), tftp (Trivial File Transfer Protocol), vat (Visual Audio Tool), vxlan (Virtual eXtensible Local Area Network), wb (distributed White Board) and zmtp1 (ZeroMQ Message Transport Protocol 1.0).

Note that the pgm type above affects UDP interpretation only, the native PGM is always recognised as IP protocol 113 regardless. UDP-encapsulated PGM is often called "EPGM" or "PGM/UDP".

Note that the pgm_zmtp1 type above affects interpretation of both native PGM and UDP at once. During the native PGM decoding the application data of an ODATA/RDATA packet would be decoded as a ZeroMQ datagram with ZMTP/1.0 frames. During the UDP decoding in addition to that any UDP packet would be treated as an encapsulated PGM packet.

-t

Don't print a timestamp on each dump line.

-tt

Print the timestamp, as seconds since January 1, 1970, 00:00:00, UTC, and fractions of a second since that time, on each dump line.

-ttt

Print a delta (microsecond or nanosecond resolution depending on the --time-stamp-precision option) between current and previous line on each dump line. The default is microsecond resolution.

-tttt

Print a timestamp, as hours, minutes, seconds, and fractions of a second since midnight, preceded by the date, on each dump line.

-ttttt

Print a delta (microsecond or nanosecond resolution depending on the --time-stamp-precision option) between current and first line on each dump line. The default is microsecond resolution.

-u

Print undecoded NFS handles.

-U

--packet-buffered

If the -w option is not specified, or if it is specified but the --print flag is also specified, make the printed packet output ``packet-buffered''; i.e., as the description of the contents of each packet is printed, it will be written to the standard output, rather than, when not writing to a terminal, being written only when the output buffer fills.

If the -w option is specified, make the saved raw packet output ``packet-buffered''; i.e., as each packet is saved, it will be written to the output file, rather than being written only when the output buffer fills.

The -U flag will not be supported if tcpdump was built with an older version of libpcap that lacks the pcap_dump_flush(3PCAP) function.

-v

When parsing and printing, produce (slightly more) verbose output. For example, the time to live, identification, total length and options in an IP packet are printed. Also enables additional packet integrity checks such as verifying the IP and ICMP header checksum.

When writing to a file with the -w option and at the same time not reading from a file with the -r option, report to stderr, once per second, the number of packets captured. In Solaris, FreeBSD and possibly other operating systems this periodic update currently can cause loss of captured packets on their way from the kernel to tcpdump.

-vv

Even more verbose output. For example, additional fields are printed from NFS reply packets, and SMB packets are fully decoded.

-vvv

Even more verbose output. For example, telnet SB ... SE options are printed in full. With -X Telnet options are printed in hex as well.

-V file

Read a list of filenames from file. Standard input is used if file is ``-''.

-w file

Write the raw packets to file rather than parsing and printing them out. They can later be printed with the -r option. Standard output is used if file is ``-''.

This output will be buffered if written to a file or pipe, so a program reading from the file or pipe may not see packets for an arbitrary amount of time after they are received. Use the -U flag to cause packets to be written as soon as they are received.

The MIME type application/vnd.tcpdump.pcap has been registered with IANA for pcap files. The filename extension .pcap appears to be the most commonly used along with .cap and .dmp. Tcpdump itself doesn't check the extension when reading capture files and doesn't add an extension when writing them (it uses magic numbers in the file header instead). However, many operating systems and applications will use the extension if it is present and adding one (e.g. .pcap) is recommended.

See pcap-savefile(5) for a description of the file format.

-W filecount

Used in conjunction with the -C option, this will limit the number of files created to the specified number, and begin overwriting files from the beginning, thus creating a 'rotating' buffer. In addition, it will name the files with enough leading 0s to support the maximum number of files, allowing them to sort correctly.

Used in conjunction with the -G option, this will limit the number of rotated dump files that get created, exiting with status 0 when reaching the limit.

If used in conjunction with both -C and -G, the -W option will currently be ignored, and will only affect the file name.

-x

When parsing and printing, in addition to printing the headers of each packet, print the data of each packet (minus its link level header) in hex. The smaller of the entire packet or snaplen bytes will be printed. Note that this is the entire link-layer packet, so for link layers that pad (e.g. Ethernet), the padding bytes will also be printed when the higher layer packet is shorter than the required padding. In the current implementation this flag may have the same effect as -xx if the packet is truncated.

-xx

When parsing and printing, in addition to printing the headers of each packet, print the data of each packet, including its link level header, in hex.

-X

When parsing and printing, in addition to printing the headers of each packet, print the data of each packet (minus its link level header) in hex and ASCII. This is very handy for analysing new protocols. In the current implementation this flag may have the same effect as -XX if the packet is truncated.

-XX

When parsing and printing, in addition to printing the headers of each packet, print the data of each packet, including its link level header, in hex and ASCII.

-y datalinktype

--linktype=datalinktype

Set the data link type to use while capturing packets (see -L) or just compiling and dumping packet-matching code (see -d) to datalinktype.

-z postrotate-command

Used in conjunction with the -C or -G options, this will make tcpdump run " postrotate-command file " where file is the savefile being closed after each rotation. For example, specifying -z gzip or -z bzip2 will compress each savefile using gzip or bzip2.

Note that tcpdump will run the command in parallel to the capture, using the lowest priority so that this doesn't disturb the capture process.

And in case you would like to use a command that itself takes flags or different arguments, you can always write a shell script that will take the savefile name as the only argument, make the flags & arguments arrangements and execute the command that you want.

-Z user

--relinquish-privileges=user

If tcpdump is running as root, after opening the capture device or input savefile, but before opening any savefiles for output, change the user ID to user and the group ID to the primary group of user.

This behavior is enabled by default (-Z tcpdump), and can be disabled by -Z root.

expression

selects which packets will be dumped. If no expression is given, all packets on the net will be dumped. Otherwise, only packets for which expression is `true' will be dumped. For the expression syntax, see pcap-filter(7).

The expression argument can be passed to tcpdump as either a single Shell argument, or as multiple Shell arguments, whichever is more convenient. Generally, if the expression contains Shell metacharacters, such as backslashes used to escape protocol names, it is easier to pass it as a single, quoted argument rather than to escape the Shell metacharacters. Multiple arguments are concatenated with spaces before being parsed.

## EXAMPLES
To print all packets arriving at or departing from sundown:

```
tcpdump host sundown
```

To print traffic between helios and either hot or ace:

```
tcpdump host helios and \( hot or ace \)
```

To print all IP packets between ace and any host except helios:

```
tcpdump ip host ace and not helios
```

To print all traffic between local hosts and hosts at Berkeley:

```
tcpdump net ucb-ether
```

To print all ftp traffic through internet gateway snup: (note that the expression is quoted to prevent the shell from (mis-)interpreting the parentheses):

```
tcpdump 'gateway snup and (port ftp or ftp-data)'
```

To print traffic neither sourced from nor destined for local hosts (if you gateway to one other net, this stuff should never make it onto your local net).

```
tcpdump ip and not net localnet
```

To print the start and end packets (the SYN and FIN packets) of each TCP conversation that involves a non-local host.

```
tcpdump 'tcp[tcpflags] & (tcp-syn|tcp-fin) != 0 and not src and dst net localnet'
```

To print the TCP packets with flags RST and ACK both set. (i.e. select only the RST and ACK flags in the flags field, and if the result is "RST and ACK both set", match)

```
tcpdump 'tcp[tcpflags] & (tcp-rst|tcp-ack) == (tcp-rst|tcp-ack)'
```

To print all IPv4 HTTP packets to and from port 80, i.e. print only packets that contain data, not, for example, SYN and FIN packets and ACK-only packets. (IPv6 is left as an exercise for the reader.)

```
tcpdump 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)'
```

To print IP packets longer than 576 bytes sent through gateway snup:

```
tcpdump 'gateway snup and ip[2:2] > 576'
```

To print IP broadcast or multicast packets that were not sent via Ethernet broadcast or multicast:

```
tcpdump 'ether[0] & 1 = 0 and ip[16] >= 224'
```

To print all ICMP packets that are not echo requests/replies (i.e., not ping packets):

```
tcpdump 'icmp[icmptype] != icmp-echo and icmp[icmptype] != icmp-echoreply'
```

## OUTPUT FORMAT
The output of tcpdump is protocol dependent. The following gives a brief description and examples of most of the formats.

### Timestamps
By default, all output lines are preceded by a timestamp. The timestamp is the current clock time in the form

```
hh:mm:ss.frac
```

and is as accurate as the kernel's clock. The timestamp reflects the time the kernel applied a time stamp to the packet. No attempt is made to account for the time lag between when the network interface finished receiving the packet from the network and when the kernel applied a time stamp to the packet; that time lag could include a delay between the time when the network interface finished receiving a packet from the network and the time when an interrupt was delivered to the kernel to get it to read the packet and a delay between the time when the kernel serviced the `new packet' interrupt and the time when it applied a time stamp to the packet.

### Interface
When the any interface is selected on capture or when a link-type LINUX_SLL2 capture file is read the interface name is printed after the timestamp. This is followed by the packet type with In and Out denoting a packet destined for this host or originating from this host respectively. Other possible values are B for broadcast packets, M for multicast packets, and P for packets destined for other hosts.

### Link Level Headers
If the '-e' option is given, the link level header is printed out. On Ethernets, the source and destination addresses, protocol, and packet length are printed.

On FDDI networks, the '-e' option causes tcpdump to print the `frame control' field, the source and destination addresses, and the packet length. (The `frame control' field governs the interpretation of the rest of the packet. Normal packets (such as those containing IP datagrams) are `async' packets, with a priority value between 0 and 7; for example, `async4'. Such packets are assumed to contain an 802.2 Logical Link Control (LLC) packet; the LLC header is printed if it is not an ISO datagram or a so-called SNAP packet.

On Token Ring networks, the '-e' option causes tcpdump to print the `access control' and `frame control' fields, the source and destination addresses, and the packet length. As on FDDI networks, packets are assumed to contain an LLC packet. Regardless of whether the '-e' option is specified or not, the source routing information is printed for source-routed packets.

On 802.11 networks, the '-e' option causes tcpdump to print the `frame control' fields, all of the addresses in the 802.11 header, and the packet length. As on FDDI networks, packets are assumed to contain an LLC packet.

(N.B.: The following description assumes familiarity with the SLIP compression algorithm described in RFC 1144.)

On SLIP links, a direction indicator (``I'' for inbound, ``O'' for outbound), packet type, and compression information are printed out. The packet type is printed first. The three types are ip, utcp, and ctcp. No further link information is printed for ip packets. For TCP packets, the connection identifier is printed following the type. If the packet is compressed, its encoded header is printed out. The special cases are printed out as *S+n and *SA+n, where n is the amount by which the sequence number (or sequence number and ack) has changed. If it is not a special case, zero or more changes are printed. A change is indicated by U (urgent pointer), W (window), A (ack), S (sequence number), and I (packet ID), followed by a delta (+n or -n), or a new value (=n). Finally, the amount of data in the packet and compressed header length are printed.

For example, the following line shows an outbound compressed TCP packet, with an implicit connection identifier; the ack has changed by 6, the sequence number by 49, and the packet ID by 6; there are 3 bytes of data and 6 bytes of compressed header:

```
O ctcp * A+6 S+49 I+6 3 (6)
```

### ARP/RARP Packets
ARP/RARP output shows the type of request and its arguments. The format is intended to be self explanatory. Here is a short sample taken from the start of an `rlogin' from host rtsg to host csam:

```
arp who-has csam tell rtsg
arp reply csam is-at CSAM
```

The first line says that rtsg sent an ARP packet asking for the Ethernet address of internet host csam. Csam replies with its Ethernet address (in this example, Ethernet addresses are in caps and internet addresses in lower case). This would look less redundant if we had done tcpdump -n:

```
arp who-has 128.3.254.6 tell 128.3.254.68
arp reply 128.3.254.6 is-at 02:07:01:00:01:c4
```

If we had done tcpdump -e, the fact that the first packet is broadcast and the second is point-to-point would be visible:

```
RTSG Broadcast 0806  64: arp who-has csam tell rtsg
CSAM RTSG 0806  64: arp reply csam is-at CSAM
```

For the first packet this says the Ethernet source address is RTSG, the destination is the Ethernet broadcast address, the type field contained hex 0806 (type ETHER_ARP) and the total length was 64 bytes.

### IPv4 Packets
If the link-layer header is not being printed, for IPv4 packets, IP is printed after the time stamp.

If the -v flag is specified, information from the IPv4 header is shown in parentheses after the IP or the link-layer header. The general format of this information is:

```
tos tos, ttl ttl, id id, offset offset, flags [flags], proto proto, length length, options (options)
```

tos is the type of service field; if the ECN bits are non-zero, those are reported as ECT(1), ECT(0), or CE. ttl is the time-to-live; it is not reported if it is zero. id is the IP identification field. offset is the fragment offset field; it is printed whether this is part of a fragmented datagram or not. flags are the MF and DF flags; + is reported if MF is set, and DF is reported if F is set. If neither are set, . is reported. proto is the protocol ID field. length is the total length field; if the packet is a presumed TSO (TCP Segmentation Offload) send, [was 0, presumed TSO] is reported. options are the IP options, if any. Next, for TCP and UDP packets, the source and destination IP addresses and TCP or UDP ports, with a dot between each IP address and its corresponding port, will be printed, with a > separating the source and destination. For other protocols, the addresses will be printed, with a > separating the source and destination. Higher level protocol information, if any, will be printed after that.

For fragmented IP datagrams, the first fragment contains the higher level protocol header; fragments after the first contain no higher level protocol header. Fragmentation information will be printed only with the -v flag, in the IP header information, as described above.

### TCP Packets
(N.B.:The following description assumes familiarity with the TCP protocol described in RFC 793. If you are not familiar with the protocol, this description will not be of much use to you.)

The general format of a TCP protocol line is:

```
src > dst: Flags [tcpflags], seq data-seqno, ack ackno, win window, urg urgent, options [opts], length len
```

Src and dst are the source and destination IP addresses and ports. Tcpflags are some combination of S (SYN), F (FIN), P (PSH), R (RST), U (URG), W (CWR), E (ECE) or `.' (ACK), or `none' if no flags are set. Data-seqno describes the portion of sequence space covered by the data in this packet (see example below). Ackno is sequence number of the next data expected the other direction on this connection. Window is the number of bytes of receive buffer space available the other direction on this connection. Urg indicates there is `urgent' data in the packet. Opts are TCP options (e.g., mss 1024). Len is the length of payload data. Iptype, Src, dst, and flags are always present. The other fields depend on the contents of the packet's TCP protocol header and are output only if appropriate.

Here is the opening portion of an rlogin from host rtsg to host csam.

```
IP rtsg.1023 > csam.login: Flags [S], seq 768512:768512, win 4096, opts [mss 1024]
IP csam.login > rtsg.1023: Flags [S.], seq, 947648:947648, ack 768513, win 4096, opts [mss 1024]
IP rtsg.1023 > csam.login: Flags [.], ack 1, win 4096
IP rtsg.1023 > csam.login: Flags [P.], seq 1:2, ack 1, win 4096, length 1
IP csam.login > rtsg.1023: Flags [.], ack 2, win 4096
IP rtsg.1023 > csam.login: Flags [P.], seq 2:21, ack 1, win 4096, length 19
IP csam.login > rtsg.1023: Flags [P.], seq 1:2, ack 21, win 4077, length 1
IP csam.login > rtsg.1023: Flags [P.], seq 2:3, ack 21, win 4077, urg 1, length 1
IP csam.login > rtsg.1023: Flags [P.], seq 3:4, ack 21, win 4077, urg 1, length 1
```

The first line says that TCP port 1023 on rtsg sent a packet to port login on csam. The S indicates that the SYN flag was set. The packet sequence number was 768512 and it contained no data. (The notation is `first:last' which means `sequence numbers first up to but not including last'.) There was no piggy-backed ACK, the available receive window was 4096 bytes and there was a max-segment-size option requesting an MSS of 1024 bytes. Csam replies with a similar packet except it includes a piggy-backed ACK for rtsg's SYN. Rtsg then ACKs csam's SYN. The `.' means the ACK flag was set. The packet contained no data so there is no data sequence number or length. Note that the ACK sequence number is a small integer (1). The first time tcpdump sees a TCP `conversation', it prints the sequence number from the packet. On subsequent packets of the conversation, the difference between the current packet's sequence number and this initial sequence number is printed. This means that sequence numbers after the first can be interpreted as relative byte positions in the conversation's data stream (with the first data byte each direction being `1'). `-S' will override this feature, causing the original sequence numbers to be output.

On the 6th line, rtsg sends csam 19 bytes of data (bytes 2 through 20 in the rtsg → csam side of the conversation). The PSH flag is set in the packet. On the 7th line, csam says it's received data sent by rtsg up to but not including byte 21. Most of this data is apparently sitting in the socket buffer since csam's receive window has gotten 19 bytes smaller. Csam also sends one byte of data to rtsg in this packet. On the 8th and 9th lines, csam sends two bytes of urgent, pushed data to rtsg.

If the snapshot was small enough that tcpdump didn't capture the full TCP header, it interprets as much of the header as it can and then reports ``[|tcp]'' to indicate the remainder could not be interpreted. If the header contains a bogus option (one with a length that's either too small or beyond the end of the header), tcpdump reports it as ``[bad opt]'' and does not interpret any further options (since it's impossible to tell where they start). If the header length indicates options are present but the IP datagram length is not long enough for the options to actually be there, tcpdump reports it as ``[bad hdr length]''.

### Particular TCP Flag Combinations (SYN-ACK, URG-ACK, etc.)
There are 8 bits in the control bits section of the TCP header:

CWR | ECE | URG | ACK | PSH | RST | SYN | FIN

Let's assume that we want to watch packets used in establishing a TCP connection. Recall that TCP uses a 3-way handshake protocol when it initializes a new connection; the connection sequence with regard to the TCP control bits is

1) Caller sends SYN

2) Recipient responds with SYN, ACK

3) Caller sends ACK

Now we're interested in capturing packets that have only the SYN bit set (Step 1). Note that we don't want packets from step 2 (SYN-ACK), just a plain initial SYN. What we need is a correct filter expression for tcpdump.

Recall the structure of a TCP header without options:

```
 0                            15                              31
-----------------------------------------------------------------
|          source port          |       destination port        |
-----------------------------------------------------------------
|                        sequence number                        |
-----------------------------------------------------------------
|                     acknowledgment number                     |
-----------------------------------------------------------------
|  HL   | rsvd  |C|E|U|A|P|R|S|F|        window size            |
-----------------------------------------------------------------
|         TCP checksum          |       urgent pointer          |
-----------------------------------------------------------------
```

A TCP header usually holds 20 octets of data, unless options are present. The first line of the graph contains octets 0 - 3, the second line shows octets 4 - 7 etc.

Starting to count with 0, the relevant TCP control bits are contained in octet 13:

```
 0             7|             15|             23|             31
----------------|---------------|---------------|----------------
|  HL   | rsvd  |C|E|U|A|P|R|S|F|        window size            |
----------------|---------------|---------------|----------------
|               |  13th octet   |               |               |
```

Let's have a closer look at octet no. 13:

```
                |               |

                |---------------|

                |C|E|U|A|P|R|S|F|

                |---------------|

                |7   5   3     0|
```

These are the TCP control bits we are interested in. We have numbered the bits in this octet from 0 to 7, right to left, so the PSH bit is bit number 3, while the URG bit is number 5.

Recall that we want to capture packets with only SYN set. Let's see what happens to octet 13 if a TCP datagram arrives with the SYN bit set in its header:

```
                |C|E|U|A|P|R|S|F|

                |---------------|

                |0 0 0 0 0 0 1 0|

                |---------------|

                |7 6 5 4 3 2 1 0|
```

Looking at the control bits section we see that only bit number 1 (SYN) is set.

Assuming that octet number 13 is an 8-bit unsigned integer in network byte order, the binary value of this octet is

00000010

and its decimal representation is

```
   7     6     5     4     3     2     1     0
0*2 + 0*2 + 0*2 + 0*2 + 0*2 + 0*2 + 1*2 + 0*2  =  2
```

We're almost done, because now we know that if only SYN is set, the value of the 13th octet in the TCP header, when interpreted as a 8-bit unsigned integer in network byte order, must be exactly 2.

This relationship can be expressed as

tcp[13] == 2

We can use this expression as the filter for tcpdump in order to watch packets which have only SYN set:

tcpdump -i xl0 'tcp[13] == 2'

The expression says "let the 13th octet of a TCP datagram have the decimal value 2", which is exactly what we want.

Now, let's assume that we need to capture SYN packets, but we don't care if ACK or any other TCP control bit is set at the same time. Let's see what happens to octet 13 when a TCP datagram with SYN-ACK set arrives:

```
     |C|E|U|A|P|R|S|F|

     |---------------|

     |0 0 0 1 0 0 1 0|

     |---------------|

     |7 6 5 4 3 2 1 0|
```

Now bits 1 and 4 are set in the 13th octet. The binary value of octet 13 is

00010010

which translates to decimal

```
   7     6     5     4     3     2     1     0
0*2 + 0*2 + 0*2 + 1*2 + 0*2 + 0*2 + 1*2 + 0*2   = 18
```

Now we can't just use 'tcp[13] == 18' in the tcpdump filter expression, because that would select only those packets that have SYN-ACK set, but not those with only SYN set. Remember that we don't care if ACK or any other control bit is set as long as SYN is set.

In order to achieve our goal, we need to logically AND the binary value of octet 13 with some other value to preserve the SYN bit. We know that we want SYN to be set in any case, so we'll logically AND the value in the 13th octet with the binary value of a SYN:

```
          00010010 SYN-ACK              00000010 SYN

     AND  00000010 (we want SYN)   AND  00000010 (we want SYN)

          --------                      --------

     =    00000010                 =    00000010
```

We see that this AND operation delivers the same result regardless whether ACK or another TCP control bit is set. The decimal representation of the AND value as well as the result of this operation is 2 (binary 00000010), so we know that for packets with SYN set the following relation must hold true:

( ( value of octet 13 ) AND ( 2 ) ) == ( 2 )

This points us to the tcpdump filter expression

tcpdump -i xl0 'tcp[13] & 2 == 2'

Some offsets and field values may be expressed as names rather than as numeric values. For example tcp[13] may be replaced with tcp[tcpflags]. The following TCP flag field values are also available: tcp-fin, tcp-syn, tcp-rst, tcp-push, tcp-ack, tcp-urg, tcp-ece and tcp-cwr.

This can be demonstrated as:

tcpdump -i xl0 'tcp[tcpflags] & tcp-push != 0'

Note that you should use single quotes or a backslash in the expression to hide the AND ('&') special character from the shell.

### UDP Packets
UDP format is illustrated by this rwho packet:

```
actinide.who > broadcast.who: udp 84
```

This says that port who on host actinide sent a UDP datagram to port who on host broadcast, the Internet broadcast address. The packet contained 84 bytes of user data. Some UDP services are recognized (from the source or destination port number) and the higher level protocol information printed. In particular, Domain Name service requests (RFC 1034/1035) and Sun RPC calls (RFC 1050) to NFS.

### TCP or UDP Name Server Requests
(N.B.:The following description assumes familiarity with the Domain Service protocol described in RFC 1035. If you are not familiar with the protocol, the following description will appear to be written in Greek.)

Name server requests are formatted as

```
src > dst: id op? flags qtype qclass name (len)

h2opolo.1538 > helios.domain: 3+ A? ucbvax.berkeley.edu. (37)
```

Host h2opolo asked the domain server on helios for an address record (qtype=A) associated with the name ucbvax.berkeley.edu. The query id was `3'. The `+' indicates the recursion desired flag was set. The query length was 37 bytes, excluding the TCP or UDP and IP protocol headers. The query operation was the normal one, Query, so the op field was omitted. If the op had been anything else, it would have been printed between the `3' and the `+'. Similarly, the qclass was the normal one, C_IN, and omitted. Any other qclass would have been printed immediately after the `A'. A few anomalies are checked and may result in extra fields enclosed in square brackets: If a query contains an answer, authority records or additional records section, ancount, nscount, or arcount are printed as `[na]', `[nn]' or `[nau]' where n is the appropriate count. If any of the response bits are set (AA, RA or rcode) or any of the `must be zero' bits are set in bytes two and three, `[b2&3=x]' is printed, where x is the hex value of header bytes two and three.

### TCP or UDP Name Server Responses
Name server responses are formatted as

```
src > dst:  id op rcode flags a/n/au type class data (len)

helios.domain > h2opolo.1538: 3 3/3/7 A 128.32.137.3 (273)
helios.domain > h2opolo.1537: 2 NXDomain* 0/1/0 (97)
```

In the first example, helios responds to query id 3 from h2opolo with 3 answer records, 3 name server records and 7 additional records. The first answer record is type A (address) and its data is internet address 128.32.137.3. The total size of the response was 273 bytes, excluding TCP or UDP and IP headers. The op (Query) and response code (NoError) were omitted, as was the class (C_IN) of the A record. In the second example, helios responds to query 2 with a response code of nonexistent domain (NXDomain) with no answers, one name server and no authority records. The `*' indicates that the authoritative answer bit was set. Since there were no answers, no type, class or data were printed.

Other flag characters that might appear are `-' (recursion available, RA, not set) and `|' (truncated message, TC, set). If the `question' section doesn't contain exactly one entry, `[nq]' is printed.

### SMB/CIFS Decoding
tcpdump now includes fairly extensive SMB/CIFS/NBT decoding for data on UDP/137, UDP/138 and TCP/139. Some primitive decoding of IPX and NetBEUI SMB data is also done.

By default a fairly minimal decode is done, with a much more detailed decode done if -v is used. Be warned that with -v a single SMB packet may take up a page or more, so only use -v if you really want all the gory details.

For information on SMB packet formats and what all the fields mean see https://download.samba.org/pub/samba/specs/ and other online resources. The SMB patches were written by Andrew Tridgell (tridge@samba.org).

### NFS Requests and Replies
Sun NFS (Network File System) requests and replies are printed as:

```
src.sport > dst.nfs: NFS request xid xid len op args
src.nfs > dst.dport: NFS reply xid xid reply stat len op results

sushi.1023 > wrl.nfs: NFS request xid 26377
	112 readlink fh 21,24/10.73165
wrl.nfs > sushi.1023: NFS reply xid 26377
	reply ok 40 readlink "../var"
sushi.1022 > wrl.nfs: NFS request xid 8219
	144 lookup fh 9,74/4096.6878 "xcolors"
wrl.nfs > sushi.1022: NFS reply xid 8219
	reply ok 128 lookup fh 9,74/4134.3150
```

In the first line, host sushi sends a transaction with id 26377 to wrl. The request was 112 bytes, excluding the UDP and IP headers. The operation was a readlink (read symbolic link) on file handle (fh) 21,24/10.731657119. (If one is lucky, as in this case, the file handle can be interpreted as a major,minor device number pair, followed by the inode number and generation number.) In the second line, wrl replies `ok' with the same transaction id and the contents of the link. In the third line, sushi asks (using a new transaction id) wrl to lookup the name `xcolors' in directory file 9,74/4096.6878. In the fourth line, wrl sends a reply with the respective transaction id.

Note that the data printed depends on the operation type. The format is intended to be self explanatory if read in conjunction with an NFS protocol spec. Also note that older versions of tcpdump printed NFS packets in a slightly different format: the transaction id (xid) would be printed instead of the non-NFS port number of the packet.

If the -v (verbose) flag is given, additional information is printed. For example:

```
sushi.1023 > wrl.nfs: NFS request xid 79658
	148 read fh 21,11/12.195 8192 bytes @ 24576
wrl.nfs > sushi.1023: NFS reply xid 79658
	reply ok 1472 read REG 100664 ids 417/0 sz 29388
```

(-v also prints the IP header TTL, ID, length, and fragmentation fields, which have been omitted from this example.) In the first line, sushi asks wrl to read 8192 bytes from file 21,11/12.195, at byte offset 24576. Wrl replies `ok'; the packet shown on the second line is the first fragment of the reply, and hence is only 1472 bytes long (the other bytes will follow in subsequent fragments, but these fragments do not have NFS or even UDP headers and so might not be printed, depending on the filter expression used). Because the -v flag is given, some of the file attributes (which are returned in addition to the file data) are printed: the file type (``REG'', for regular file), the file mode (in octal), the UID and GID, and the file size. If the -v flag is given more than once, even more details are printed.

NFS reply packets do not explicitly identify the RPC operation. Instead, tcpdump keeps track of ``recent'' requests, and matches them to the replies using the transaction ID. If a reply does not closely follow the corresponding request, it might not be parsable.

### AFS Requests and Replies
Transarc AFS (Andrew File System) requests and replies are printed as:

```
src.sport > dst.dport: rx packet-type
src.sport > dst.dport: rx packet-type service call call-name args
src.sport > dst.dport: rx packet-type service reply call-name args

elvis.7001 > pike.afsfs:
	rx data fs call rename old fid 536876964/1/1 ".newsrc.new"
	new fid 536876964/1/1 ".newsrc"
pike.afsfs > elvis.7001: rx data fs reply rename
```

In the first line, host elvis sends a RX packet to pike. This was a RX data packet to the fs (fileserver) service, and is the start of an RPC call. The RPC call was a rename, with the old directory file id of 536876964/1/1 and an old filename of `.newsrc.new', and a new directory file id of 536876964/1/1 and a new filename of `.newsrc'. The host pike responds with a RPC reply to the rename call (which was successful, because it was a data packet and not an abort packet). In general, all AFS RPCs are decoded at least by RPC call name. Most AFS RPCs have at least some of the arguments decoded (generally only the `interesting' arguments, for some definition of interesting).

The format is intended to be self-describing, but it will probably not be useful to people who are not familiar with the workings of AFS and RX.

If the -v (verbose) flag is given twice, acknowledgement packets and additional header information is printed, such as the RX call ID, call number, sequence number, serial number, and the RX packet flags.

If the -v flag is given twice, additional information is printed, such as the RX call ID, serial number, and the RX packet flags. The MTU negotiation information is also printed from RX ack packets.

If the -v flag is given three times, the security index and service id are printed.

Error codes are printed for abort packets, with the exception of Ubik beacon packets (because abort packets are used to signify a yes vote for the Ubik protocol).

AFS reply packets do not explicitly identify the RPC operation. Instead, tcpdump keeps track of ``recent'' requests, and matches them to the replies using the call number and service ID. If a reply does not closely follow the corresponding request, it might not be parsable.

### KIP AppleTalk (DDP in UDP)
AppleTalk DDP packets encapsulated in UDP datagrams are de-encapsulated and dumped as DDP packets (i.e., all the UDP header information is discarded). The file /etc/atalk.names is used to translate AppleTalk net and node numbers to names. Lines in this file have the form

```
number	name
1.254		ether
16.1		icsd-net
1.254.110	ace
```

The first two lines give the names of AppleTalk networks. The third line gives the name of a particular host (a host is distinguished from a net by the 3rd octet in the number - a net number must have two octets and a host number must have three octets.) The number and name should be separated by whitespace (blanks or tabs). The /etc/atalk.names file may contain blank lines or comment lines (lines starting with a `#'). AppleTalk addresses are printed in the form

```
net.host.port
144.1.209.2 > icsd-net.112.220
office.2 > icsd-net.112.220
jssmag.149.235 > icsd-net.2
```

(If the /etc/atalk.names doesn't exist or doesn't contain an entry for some AppleTalk host/net number, addresses are printed in numeric form.) In the first example, NBP (DDP port 2) on net 144.1 node 209 is sending to whatever is listening on port 220 of net icsd node 112. The second line is the same except the full name of the source node is known (`office'). The third line is a send from port 235 on net jssmag node 149 to broadcast on the icsd-net NBP port (note that the broadcast address (255) is indicated by a net name with no host number - for this reason it's a good idea to keep node names and net names distinct in /etc/atalk.names). NBP (name binding protocol) and ATP (AppleTalk transaction protocol) packets have their contents interpreted. Other protocols just dump the protocol name (or number if no name is registered for the protocol) and packet size.

### NBP Packets
NBP packets are formatted like the following examples:

```
icsd-net.112.220 > jssmag.2: nbp-lkup 190: "=:LaserWriter@*"
jssmag.209.2 > icsd-net.112.220: nbp-reply 190: "RM1140:LaserWriter@*" 250
techpit.2 > icsd-net.112.220: nbp-reply 190: "techpit:LaserWriter@*" 186
```

The first line is a name lookup request for laserwriters sent by net icsd host 112 and broadcast on net jssmag. The nbp id for the lookup is 190. The second line shows a reply for this request (note that it has the same id) from host jssmag.209 saying that it has a laserwriter resource named "RM1140" registered on port 250. The third line is another reply to the same request saying host techpit has laserwriter "techpit" registered on port 186.

### ATP Packets
ATP packet formatting is demonstrated by the following example:

```
jssmag.209.165 > helios.132: atp-req  12266<0-7> 0xae030001
helios.132 > jssmag.209.165: atp-resp 12266:0 (512) 0xae040000
helios.132 > jssmag.209.165: atp-resp 12266:1 (512) 0xae040000
helios.132 > jssmag.209.165: atp-resp 12266:2 (512) 0xae040000
helios.132 > jssmag.209.165: atp-resp 12266:3 (512) 0xae040000
helios.132 > jssmag.209.165: atp-resp 12266:4 (512) 0xae040000
helios.132 > jssmag.209.165: atp-resp 12266:5 (512) 0xae040000
helios.132 > jssmag.209.165: atp-resp 12266:6 (512) 0xae040000
helios.132 > jssmag.209.165: atp-resp*12266:7 (512) 0xae040000
jssmag.209.165 > helios.132: atp-req  12266<3,5> 0xae030001
helios.132 > jssmag.209.165: atp-resp 12266:3 (512) 0xae040000
helios.132 > jssmag.209.165: atp-resp 12266:5 (512) 0xae040000
jssmag.209.165 > helios.132: atp-rel  12266<0-7> 0xae030001
jssmag.209.133 > helios.132: atp-req* 12267<0-7> 0xae030002
```

Jssmag.209 initiates transaction id 12266 with host helios by requesting up to 8 packets (the `<0-7>'). The hex number at the end of the line is the value of the `userdata' field in the request. Helios responds with 8 512-byte packets. The `:digit' following the transaction id gives the packet sequence number in the transaction and the number in parens is the amount of data in the packet, excluding the ATP header. The `*' on packet 7 indicates that the EOM bit was set.

Jssmag.209 then requests that packets 3 & 5 be retransmitted. Helios resends them then jssmag.209 releases the transaction. Finally, jssmag.209 initiates the next request. The `*' on the request indicates that XO (`exactly once') was not set.

## BACKWARD COMPATIBILITY
The TCP flag names tcp-ece and tcp-cwr became available when linking with libpcap 1.9.0 or later.

## SEE ALSO
stty(1), pcap(3PCAP), bpf(4), nit(4P), pcap-savefile(5), pcap-filter(7), pcap-tstamp(7)

https://www.iana.org/assignments/media-types/application/vnd.tcpdump.pcap

## AUTHORS
The original authors are:

Van Jacobson, Craig Leres and Steven McCanne, all of the Lawrence Berkeley National Laboratory, University of California, Berkeley, CA.

It is currently maintained by The Tcpdump Group.

The current version is available via HTTPS:

https://www.tcpdump.org/

The original distribution is available via anonymous ftp:

ftp://ftp.ee.lbl.gov/old/tcpdump.tar.Z

IPv6/IPsec support is added by WIDE/KAME project. This program uses OpenSSL/LibreSSL, under specific configurations.

## BUGS
To report a security issue please send an e-mail to security@tcpdump.org.

To report bugs and other problems, contribute patches, request a feature, provide generic feedback etc. please see the file CONTRIBUTING.md in the tcpdump source tree root.

NIT doesn't let you watch your own outbound traffic, BPF will. We recommend that you use the latter.

Some attempt should be made to reassemble IP fragments or, at least to compute the right length for the higher level protocol.

Name server inverse queries are not dumped correctly: the (empty) question section is printed rather than real query in the answer section. Some believe that inverse queries are themselves a bug and prefer to fix the program generating them rather than tcpdump.

A packet trace that crosses a daylight savings time change will give skewed time stamps (the time change is ignored).

Filter expressions on fields other than those in Token Ring headers will not correctly handle source-routed Token Ring packets.

Filter expressions on fields other than those in 802.11 headers will not correctly handle 802.11 data packets with both To DS and From DS set.

ip6 proto should chase header chain, but at this moment it does not. ip6 protochain is supplied for this behavior.

Arithmetic expression against transport layer headers, like tcp[0], does not work against IPv6 packets. It only looks at IPv4 packets.