Set_rlimits 1.2.0 review

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Set_rlimits project is a small wrapper program to allow people to take advantage of the realtime resource limit extensions available

License: GPL (GNU General Public License)
File size: 40K
Developer: Jonathan Woithe
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Set_rlimits project is a small wrapper program to allow people to take advantage of the realtime resource limit extensions available in Linux kernels 2.6.12 and later without having to resort to using a PAM module. This is of particular interest for Slackware users since Slackware doesn't use PAM, but other users may find this program helpful as well. In addition, several other resource limits can be manipulated by the program.

set_rlimits needs to be installed setuid root. However, it runs at elevated priviledges only when setting the process resource limits. This minimises potential security implications. Despite this, no security guarantee is given; users concerned about the security of this program should review the source code themselves. Suggestions on improving security are welcomed by the author.

The resource limits which set_rlimits is permitted to grant are controlled by the configuration file (CONFIG_FILE in set_rlimits.c, usually /etc/set_rlimits.conf). This file sets the maximum priorities which set_rlimits can set for a given program when executed by a given user or group. The program specified must include an absolute path. This gives an administrator fairly fine-grained control over who can execute programs at elevated priorities and which programs they are. The enforced specification of an absolute path in the configuration file means the administrator can
maintain con trol over exactly which programs may be run with elevated resource limits.

For further details on the configuration file format, refer to the samle set_rlimits.conf provided in the source distribution, or the source itself.


This program compiles and runs successfully under Slackware 10.x running a 2.6.12-rc5 kernel and above. Hopefully there are not too many distibution-specific assumptions in the source and a simple "make" will be sufficient for most people. Please don't complain that autoconf isn't used or supported; I simply don't have time to do this at the moment. However, patches to introduce such functionality would be welcome.

There is also rudimentary "make install" functionality in the Makefile. This simply copies the executable to /usr/local/bin/ and makes it setuid root, copies the manual page to /usr/local/man/man8/, and copies the sample set_rlimits.conf file to /etc/. The destination directories can be altered by editting Makefile and changing PREFIX and/or SYSCONFDIR. However, note that if an alternative configuration file location/name is desired, the CONFIG_FILE define in set_rlimits.c will need to be editted to reflect this.

Known issues:

muse 0.7.2pre1 appears to require a realtime priorty of at least 80; without this, realtime scheduling is denied (the watchdog thread actually requests a realtime priority of 100, but muse appears to run fine without this request being permitted). Even with elevated priority, when run through set_rlimits, a setuid root muse 0.7.2pre1 binary exits on startup: muse: Fatal IO error: client killed

The cause is currently not known or understood. The workaround is to not have the muse binary setuid root. This is fine, since running set_rlimits under kernel 2.6.12 or later should make it unnecessary for muse (and other low latency audio applications) to be setuid root.

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