capsh

CAPSH(1)                         User Commands                        CAPSH(1)



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
       The tool 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.

       -- [args]             Execute /bin/bash with trailing arguments. Note,
                             you can use -c 'command to execute' for specific
                             commands.

       ==                    Execute capsh again with remaining arguments.
                             Useful for testing exec() behavior.

       --caps=cap-set        Set the prevailing process capabilities to those
                             specified by cap-set.  Where cap-set is a text-
                             representation of capability state as per
                             cap_from_text(3).

       --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 the capsh program
                             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 the
                             capsh program is 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.

       --modes               Lists all of the libcap modes supported by
                             --mode.

       --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.

       --inmode=<mode>       Confirm that the prevailing mode is so named, 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 prepations
                             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 gid 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 for ways to
                             disable this feature.

       --secbits=N           Set the security-bits for the program, this is
                             via prctl(2), PR_SET_SECUREBITS API, and 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.

       --chroot=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.

       --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:  ffffffffffffffff
                              CapEff:  fffffffffffffeff
                              CapBnd:  ffffffffffffffff

                             This option provides a quick way to decode a
                             capability vector represented in this form. For
                             example, the missing capability from this
                             effective set is 0x0100. By running:

                              capsh --decode=0x0100

                             we observe that the missing capability is:
                             cap_setpcap.

       --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, the capsh
                             command exits with status 1.

       --has-a=xxx           Exit with status 1 unless the ambient vector has
                             capability xxx raised.

       --addamb=xxx          Adds the specificed 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.



       EXIT STATUS
              Following successful execution the tool exits with status 0.
              Following an error, the tool immediately exits with status 1.

AUTHOR
       Written by Andrew G. Morgan <morgan@kernel.org>.

REPORTING BUGS
       Please report bugs via:

       https://bugzilla.kernel.org/buglist.cgi?component=libcap&list_id=1047723&product=Tools&resolution=---

SEE ALSO
       libcap(3), getcap(8), setcap(8) and capabilities(7).



libcap 2                          2020-01-07                          CAPSH(1)