Libsysconfcpus Save

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by Kevin Pulo, [email protected] Copyright (c) 2008-2009 Licensed under the GNU GPL v2 or higher, as per the COPYING file.


libsysconfcpus is an $LD_PRELOAD library that intercepts calls to sysconf(), and adjusts the responses for _SC_NPROCESSORS_CONF and _SC_NPROCESSORS_ONLN, which are used to determine the number of processors available (either configured or online) at runtime in a system. Unfortunately, some closed- source software assumes that all of these processors may be used for computation, which is an assumption that is frequently not true on multiuser and HPC systems. Thus, libsysconfcpus provides a simple, non-intrusive way of adjusting the behaviour of such software (when it is dynamically linked).

In addition, libsysconfcpus is a small, simple example of how to use $LD_PRELOAD to do function call interception on glibc and POSIX systems. It is hoped that it is useful not only inherently, but also for learning about $LD_PRELOAD, and as a template or skeleton LD_PRELOAD library. Its from-scratch development was used to illustrate LD_PRELOAD usage in the "Fun with LD_PRELOAD" presentation by the author at 2009 in Hobart.


Standard autoconf process: ./configure && make && make install


sysconfcpus [options] <program> [args...]

Valid options are:

-v, --version   Display the sysconfcpus version
-h, --help      Display this help
-d, --debug     Display debug info

-n, --num <n>   Number of processors (both conf and onln)
-c, --conf <n>  Number of processors (conf(igured))
-o, --onln <n>  Number of processors (online)


$ test-sysconfcpus sysconf(_SC_NPROCESSORS_CONF) = 2 sysconf(_SC_NPROCESSORS_ONLN) = 2 $ sysconfcpus -n 8 test-sysconfcpus sysconf(_SC_NPROCESSORS_CONF) = 8 sysconf(_SC_NPROCESSORS_ONLN) = 8 $ sysconfcpus -c 8 -o 6 test-sysconfcpus sysconf(_SC_NPROCESSORS_CONF) = 8 sysconf(_SC_NPROCESSORS_ONLN) = 6 $


  • Only dynamically linked binaries


Comments, feature suggestions, bug reports, patches, etc are most welcome, please send them to Kevin Pulo [email protected].


  • ltrace
  • strace
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