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 ca-
pability testing and environment creation. It also provides some debug-
ging 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 prevail-
ing bounding set. The capabilities are a comma
separated list of capabilities as recognized by
the cap_from_name(3) function. Use of this fea-
ture 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_set-
groups(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 se-
tuid(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 pre-
vailing 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 set-
gid(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 set-
groups(2) system call. See --user for a more con-
venient way of doing this.
--keep=<0|1> In a non-pure capability mode, the kernel pro-
vides liberal privilege to the super-user. How-
ever, it is normally the case that when the su-
per-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 argu-
ment. 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 pur-
pose of this command is to support exploring the
way processes are killable in the face of capa-
bility 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 ca-
pability vector represented in this form. For ex-
ample, 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 ex-
istence of a capability on the system. For exam-
ple, --supports=cap_syslog will cause capsh to
promptly exit with a status of 1 when run on ker-
nel 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=lib-
cap&list_id=1047723&product=Tools&resolution=---
SEE ALSO
libcap(3), getcap(8), setcap(8) and capabilities(7).
libcap 2 2020-01-07 CAPSH(1)
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