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:
Following successful execution the tool exits with status 0. Following an error,
the tool immediately exits with status 1.
Written by Andrew G. Morgan <firstname.lastname@example.org>.
Please report bugs to the author.
libcap(3), getcap(8),setcap(8) and capabilities(7).
- 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
- 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 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
- 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)
- Force all gid values to equal id using the setgid(2)
- Set the supplementary groups to the numerical list provided. The groups
are set with the setgroups(2) system call.
- 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
- 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
- This is a convenience feature. If you look at /proc/1/status there
are some capability related fields of the following form:
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:
- 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.
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