# capsh

## NAME



           capsh - capability shell wrapper
    


## SYNOPSIS



           **capsh**[_OPTION_]...
    


## DESCRIPTION



           Linux capability support and use can be explored and constrained
           with this tool. This tool provides a handy wrapper for certain
           types of capability testing and environment creation. It also
           provides some debugging features useful for summarizing capability
           state.
    


## OPTIONS



           **capsh** takes a number of optional arguments, acting on them in the
           order they are provided. They are as follows:
    
           **--help** Display the list of commands supported by **capsh**.
    
           **--print**
                  Display prevailing capability and related state.
    
           **--current**
                  Display prevailing capability state, 1e capabilities and
                  IAB vector.
    
           **--**_[args]_
                  Execute **/bin/bash** with trailing arguments. Note, you can
                  use **-c 'command to execute'** for specific commands.
    
           **-+**_[args]_
                  Uses cap_launch(3) to fork a child to execute the shell.
                  When the child exits, **capsh** exits with the status of the
                  child or 1 in the case that the child was terminated by a
                  signal.
    
           **==**_[args]_
                  Execute **capsh** again with the remaining arguments. Useful
                  for testing **exec**() behavior. Note, PATH is searched when
                  the running **capsh** was found via the shell's PATH searching.
                  If the **exec** occurs after a **--chroot=**_/some/path_ argument the
                  PATH located binary may not be resolve to the same binary
                  as that running initially. This behavior is an intended
                  feature as it can complete the chroot transition.
    
           **=+**_[args]_
                  Uses cap_launch(3) to fork a child to re-execute **capsh**.
                  When this child exits, **capsh** exits with the status of the
                  child or 1 in the case that the child was terminated by a
                  signal.
    
           **--caps=**_cap-set_
                  Set the prevailing process capabilities to those specified
                  by _cap-set_.  Where _cap-set_ is a text-representation of a
                  capability `Set' as per cap_text_formats(7).
    
           **--drop=**_cap-list_
                  Remove the listed capabilities from the prevailing bounding
                  set. The capabilities are a comma-separated list of
                  capabilities as recognized by the cap_from_name(3)
                  function. Use of this feature requires that **capsh** is
                  operating with **CAP_SETPCAP** in its effective set.
    
           **--inh=**_cap-list_
                  Set the inheritable set of capabilities for the current
                  process to equal those provided in the comma separated
                  list. For this action to succeed, the prevailing process
                  should already have each of these capabilities in the union
                  of the current inheritable and permitted capability sets,
                  or **capsh** should be operating with **CAP_SETPCAP** in its
                  effective set.
    
           **--user=**_username_
                  Assume the identity of the named user. That is, look up the
                  user's UID and GID with getpwuid(3) and their group
                  memberships with getgrouplist(3) and set them all using
                  cap_setuid(3) and cap_setgroups(3).  Following this
                  command, the effective capabilities will be cleared, but
                  the permitted set will not be, so the running program is
                  still privileged.
    
           **--mode** Display the prevailing libcap mode as guessed by the
                  cap_get_mode(3) function.
    
           **--mode=** <mode>
                  Force the program into a cap_set_mode(3) security mode.
                  This is a set of securebits and prevailing capability
                  arrangement recommended for its pre-determined security
                  stance.
    
           **--modes**
                  Lists all of the libcap modes supported by **--mode=** <mode>.
    
           **--inmode=** <mode>
                  Confirm that the prevailing mode is that specified in
                  _< mode>_, or exit with a status 1.
    
           **--uid=**_id_
                  Force all UID values to equal _id_ using the setuid(2) system
                  call. This argument may require explicit preparation of the
                  effective set.
    
           **--cap-uid=** <uid>
                  use the cap_setuid(3) function to set the UID of the
                  current process. This performs all preparations for setting
                  the UID without dropping capabilities in the process.
                  Following this command the prevailing effective
                  capabilities will be lowered.
    
           **--is-uid=**_< id>_
                  Exit with status 1 unless the current UID equals _< id>_.
    
           **--gid=**_< id>_
                  Force all GID values to equal _id_ using the setgid(2) system
                  call.
    
           **--is-gid=**_< id>_
                  Exit with status 1 unless the current GIQ equals _< id>_.
    
           **--groups=**_< gid-list>_
                  Set the supplementary groups to the numerical list
                  provided. The groups are set with the setgroups(2) system
                  call. See **--user** for a more convenient way of doing this.
    
           **--keep=**_< 0|1>_
                  In a non-pure capability mode, the kernel provides liberal
                  privilege to the super-user. However, it is normally the
                  case that when the super-user changes UID to some lesser
                  user, then capabilities are dropped. For these situations,
                  the kernel can permit the process to retain its
                  capabilities after a setuid(2) system call. This feature is
                  known as _keep-caps_ support. The way to activate it using
                  this program is with this argument. Setting the value to 1
                  will cause _keep-caps_ to be active. Setting it to 0 will
                  cause keep-caps to deactivate for the current process. In
                  all cases, _keep-caps_ is deactivated when an **exec**() is
                  performed. See **--secbits** and**--mode** for ways to disable this
                  feature.
    
           **--secbits=**_N_
                  Set the security-bits for the program.  This is done using
                  the prctl(2) **PR_SET_SECUREBITS** operation.  The list of
                  supported bits and their meaning can be found in the
                  **< sys/secbits.h> **header file. The program will list these
                  bits via the **--print** command.  The argument is expressed as
                  a numeric bitmask, in any of the formats permitted by
                  strtoul(3).  An alternative to this bit-twiddling is
                  embedded in the **--mode*** commandline arguments.
    
           **--chroot=**_/some/path_
                  Execute the chroot(2) system call with the new root-
                  directory (/) equal to _path_.  This operation requires
                  **CAP_SYS_CHROOT** to be in effect.
    
           **--forkfor=**_sec_
                  This command causes the program to fork a child process for
                  so many seconds. The child will sleep that long and then
                  exit with status 0. The purpose of this command is to
                  support exploring the way processes are killable in the
                  face of capability changes. See the **--killit** command. Only
                  one fork can be active at a time.
    
           **--killit=**_sig_
                  This commands causes a **--forkfor** child to be kill(2)d with
                  the specified signal. The command then waits for the child
                  to exit.  If the exit status does not match the signal
                  being used to kill it, the **capsh** program exits with status
                  1.
    
           **--explain=**_cap_xxx_
                  Give a brief textual description of what privileges the
                  specified capability makes available to a running program.
                  Note, instead of _cap_xxx_ , one can provide a decimal number
                  and **capsh** will look up the corresponding capability's
                  description.
    
           **--shell** _=/full/path_
                  This option changes the shell that is invoked when the
                  argument **==** is encountered.
    
           **--strict**
                  This option toggles the suppression of subsequent attempts
                  to fixup **--caps=** and **--inh=** arguments. That is, when the
                  prevailing Effective flag does not contain **CAP_SETPCAP the**
                  **to be raised Inheritable Flag values (in strict mode) are**
                  **limited to those in the Permitted set. The strict mode**
                  **defaults to off. Supplying this argument an even number of**
                  **times restores this default behavior.**
    
           **--suggest=**_phrase_
                  Scan each of the textual descriptions of capabilities,
                  known to **capsh** , and display all descriptions that include
                  _phrase_.
    
           **--decode=**_N_
                  This is a convenience feature. If you look at
                  **/proc/1/status** there are some capability related fields of
                  the following form:
    
                  CapInh:   0000000000000000
                  CapPrm:   0000003fffffffff
                  CapEff:   0000003fffffffff
                  CapBnd:   0000003fffffffff
                  CapAmb:   0000000000000000
    
                  This option provides a quick way to decode a capability
                  vector represented in this hexadecimal form.  Here's an
                  example that decodes the two lowest capability bits:
    
                  $ **capsh --decode=3**
                  0x0000000000000003=cap_chown,cap_dac_override
    
           **--supports=**_xxx_
                  As the kernel evolves, more capabilities are added. This
                  option can be used to verify the existence of a capability
                  on the system. For example, **--supports=**_cap_syslog_ will
                  cause **capsh** to promptly exit with a status of 1 when run on
                  kernel 2.6.27.  However, when run on kernel 2.6.38 it will
                  silently succeed.
    
           **--has-p=**_xxx_
                  Exit with status 1 unless the _permitted_ vector has
                  capability **xxx** raised.
    
           **--has-ambient**
                  Performs a check to see if the running kernel supports
                  ambient capabilities. If not, **capsh** exits with status 1.
    
           **--has-a=**_xxx_
                  Exit with status 1 unless the _ambient_ vector has capability
                  **xxx** raised.
    
           **--has-b=**_xxx_
                  Exit with status 1 unless the _bounding_ vector has
                  capability **xxx** in its (default) non-blocked state.
    
           **--iab=**_xxx_
                  Attempts to set the IAB tuple of inheritable capability
                  vectors.  The text conventions used for _xxx_ are those of
                  cap_iab_from_text(3), and described in cap_text_formats(7).
    
           **--addamb=**_xxx_
                  Adds the specified ambient capability to the running
                  process.
    
           **--delamb=**_xxx_
                  Removes the specified ambient capability from the running
                  process.
    
           **--noamb**
                  Drops all ambient capabilities from the running process.
    
           **--noenv**
                  Suppresses overriding of the HOME and USER environment
                  variables when a subsequent **--user** argument is processed.
    
           **--quiet**
                  This argument is ignored unless it is the first one. If
                  present, it suppresses the capsh runtime check to confirm
                  the running libcap is recent enough that it can name all of
                  the kernel supported capability values.
    


## EXIT STATUS



           Following successful execution, **capsh** exits with status 0.
           Following an error, **capsh** immediately exits with status 1.
    


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