11-11-2013
Implement ps command in C
Hello, could anybody explain how the ps command works? I know something about the proc file system. But I'm still not sure about how it exactly works. Like ps without any option will print out the current user's processes, but it never displays my web browsers such as firefox or my LibreOffice while they're open.
I know all the files with numerical names are PIDs, but I don't know how the ps command differentiate them, catargorizing them according the users who fired them. Or where it gets the TTY and cpu time and CMD info.
That would be wonderful if someone could give a simple example about how to mimick the functions of ps command just by reading the proc directory(better in C). Thanks a lot.
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LEARN ABOUT DEBIAN
cpufreq-info
cpufreq-info(1) cpufreq-info(1)
NAME
cpufreq-info - Utility to retrieve cpufreq kernel information
SYNTAX
cpufreq-info [options]
DESCRIPTION
A small tool which prints out cpufreq information helpful to developers and interested users.
OPTIONS
-c --cpu <CPU>
<CPU> number which information shall be determined about.
-e --debug
Prints out debug information.
-f --freq
Get frequency the CPU currently runs at, according to the cpufreq core.
-w --hwfreq
Get frequency the CPU currently runs at, by reading it from hardware (only available to root).
-l --hwlimits
Determine the minimum and maximum CPU frequency allowed.
-d --driver
Determines the used cpufreq kernel driver.
-p --policy
Gets the currently used cpufreq policy.
-g --governors
Determines available cpufreq governors.
-a --related-cpus
Determines which CPUs run at the same hardware frequency.
-a --affected-cpus
Determines which CPUs need to have their frequency coordinated by software.
-s --stats
Shows cpufreq statistics if available.
-y --latency
Determines the maximum latency on CPU frequency changes.
-o --proc
Prints out information like provided by the /proc/cpufreq interface in 2.4. and early 2.6. kernels.
-m --human
human-readable output for the -f, -w, -s and -y parameters.
-h --help
Prints out the help screen.
REMARKS
You can't specify more than one of the output specific options -o -e -a -g -p -d -l -w -f -y.
You also can't specify the -o option combined with the -c option.
FILES
/sys/devices/system/cpu/cpu*/cpufreq/
/proc/cpufreq (deprecated)
/proc/sys/cpu/ (deprecated)
AUTHORS
Dominik Brodowski <linux@brodo.de> - author
Mattia Dongili<malattia@gmail.com> - first autolibtoolization
SEE ALSO
cpufreq-set(1), cpufreq-aperf(1)
Mattia Dongili 0.1 cpufreq-info(1)