capsh - capability shell wrapper
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.
The tool takes a number of optional arguments, acting on them in the order they
are provided. They are as follows:
- 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.
- 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).
- Remove the listed capabilities from the prevailing bounding
set. The capabilites 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.
- 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.
- 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.
- Force all uid values to equal id using the
setuid(2) system call.
- Force all gid values to equal id using the
setgid(2) system call.
- Set the supplementary groups to the numerical list
provided. The groups are set with the setgroups(2) system
- 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
script 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.
- XXX - need to document this feature.
- Execute the chroot(2) system call with the new
root-directory (/) equal to path. This operation requires
CAP_SYS_CHROOT to be in effect.
- This is a convenience feature. If you look at
/proc/1/status there are some capability related fields of the
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:
we observe that the missing capability is: cap_setpcap.
- 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.
Following successful execution the tool exits with status 0. Following an error,
the tool immediately exits with status 1.
Written by Andrew G. Morgan <email@example.com>.
Please report bugs to the author.