Process-Monitor-CLI

A small top-style process monitor for Linux, written in C. It reads /proc directly and lists each process's CPU and memory use, sorted by whichever you care about.

$ ./proc_monitor -n 6
    PID   CPU%   RSS(KiB) S NAME
   1903   28.9     127136 S Runner.Worker
    775    1.0      51196 S php-fpm8.3
    865    1.0      45944 S containerd
   1839    0.0     156364 S provjobd1861240
   1882    0.0      97844 S Runner.Listener
   1017    0.0      72660 S dockerd

Output captured on a GitHub Actions runner.

Usage

make
./proc_monitor               # every process, busiest first, measured over 1 second
./proc_monitor -n 10 -s mem  # the 10 processes using the most memory
./proc_monitor -h            # all options

Option	Meaning	Default
-i SECONDS	How long to measure CPU use for (0.1 to 60)	1
-n COUNT	Show only the first COUNT processes	all
-s cpu or -s mem	Sort by CPU or by memory	cpu

Columns: PID, CPU% (100% is one full core, as in top), RSS(KiB) (memory actually held in RAM), S (process state) and NAME.

Requires Linux, a C11 compiler and make.

How it works

• Memory is the resident set size: field 24 of /proc/[pid]/stat, a number of pages, multiplied by the page size from sysconf(_SC_PAGESIZE).
• CPU% comes from two readings of each process's CPU time (fields 14 and 15, utime and stime) taken -i seconds apart: the CPU time used in between, divided by the time that passed. This is how top measures current use.
• Names can contain spaces and parentheses (my (odd) proc), so the parser takes the name from the first ( to the last ) instead of splitting the line on spaces.
• A process that exits between readings is skipped.

Testing

make test         # unit tests: /proc parsing, CPU and memory maths
make integration  # runs the program on fixture data and checks its memory figure against ps
make sanitize     # both suites under AddressSanitizer and UndefinedBehaviorSanitizer

GitHub Actions runs all three on every push and pull request, builds with both GCC and Clang, and runs cppcheck.

Project structure

include/proc.h            parser and calculation interface
src/proc.c                /proc/[pid]/stat parser, CPU% and memory calculations
src/main.c                options, sampling, sorting and output
tests/test_proc.c         unit tests
tests/run_integration.sh  end-to-end checks
tests/fixtures/proc/      a small fake /proc tree used by the tests

Limitations

• Linux only, because it reads /proc.
• Prints one snapshot and exits; it does not refresh like top.
• A process that starts during the measuring interval is shown with 0% CPU.

License

MIT