How to get all process ids without ps command on Linux

Question

How to get all process ids (pid) (similar to: $ ps aux) but without using ps.

One example of when this would be used is when developing a dotnet 5 application to run on a docker host. The dotnet runtime image is a very cut-down Linux image, with bash, but without ps. When diagnosing an issue with the application, it's sometimes useful to see what processes are running and if separate processes have been spawned correctly. ps is unavailable on this image. Is there an alternative?

Homestead

Answer 1

On Linux, all running process have "metadata" stored in the /proc filesystem.

All running process ids:

shopt -s extglob # assuming bash
(cd /proc && echo +([0-9]))

Urano

what is the meaning of echo +([0-9]) .Thanks! – Homestead

When I open the filessystems, there are some other information but how the +([0-9]) get the pid. Thanks! Sincerely! – Homestead

That's a bash [extended filename globbing pattern]() that matches one or more digits. In the /proc directory, there is a subdirectory for each process (named with the numeric pid), and a bunch of other things – Urano

Why was this question closed as unclear? The question seems abundantly clear as evidenced by the on-point answer. Can we get this question reopened? – Particle

It was most likely closed because there is no effort made by the OP. Note the close message: "Please clarify your specific problem or add additional details to highlight exactly what you need" – Urano

Try for exe in /proc/*/exe; do ls -l $exe; done – Sower

Want tp clarify that shopt is not included on the current default dotnet docker image – Blowfish

To also show the command line that started the process, after executing shopt -s extglob on its own line, try: for exe in /proc/+([0-9])/exe; do ls -l $exe; echo "Command line with args:"; tr '\0' '\n' < $(dirname $exe)/cmdline; echo -e '\n'; done – Torpid

Answer 2

Further to the comment by @FelixJongleur42, the command

ls -l /proc/*/exe

yields a parseable output with additional info such as the process user, start time and command.

Nitriding

Answer 3

This one-liner will give you the pid and the cmd with args:

for prc in /proc/*/cmdline; { (printf "$prc "; cat -A "$prc") | sed 's/\^@/ /g;s|/proc/||;s|/cmdline||'; echo; }

Undertaking

very nice, thank you! – Saks

In debian it's for prc in /proc/*/cmdline; do (printf "$prc "; cat -A "$prc") | sed 's/\^@/ /g;s|/proc/||;s|/cmdline||'; echo; done – Squint

Answer 4

Based on Ivan's example with some filtering:

for prc in /proc/*/cmdline; { 
    (printf "$prc "; cat -A "$prc") | sed 's/\^@/ /g;s|/proc/||;s|/cmdline||' | grep java ; echo -n; 
}

Sammer