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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 pro-
vided. 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 recog-
nized by the cap_from_name(3) function. Use of this feature requires
that the capsh program is operating with CAP_SETPCAP in its effec-
tive 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 get-
grouplist(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 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 de-
activate for the current process. In all cases, keep-caps is deacti-
vated 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 ef-
fect.
--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 pro-
cesses 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 spec-
ified 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 rep-
resented 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 capa-
bilities. 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 AT kernel.org>.
REPORTING BUGS
Please report bugs via:
https://bugzilla.kernel.org/buglist.cgi?component=libcap&list_id=1047723&prod-
uct=Tools&resolution=---
SEE ALSO
libcap(3), getcap(8), setcap(8) and capabilities(7).
libcap 2 2020-01-07 CAPSH(1)
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