How can I get process name of specific PID with ps command in alpine - process

Question

In ubuntu based docker/os
$ ps
PID USER TIME COMMAND
1 postgres 0:00 postgres
47 postgres 0:00 postgres: checkpointer process
48 postgres 0:00 postgres: writer process
49 postgres 0:00 postgres: wal writer process
50 postgres 0:00 postgres: autovacuum launcher process
51 postgres 0:00 postgres: stats collector process
52 postgres 0:00 postgres: bgworker: logical replication launcher
Now If run ps -p 1 -o user=, it will get me PID 1 process USER postgres
$ ps -p 1 -o user=
postgres
This is what I can do in ubuntu based image/os
Now
I am really seeking for a way to do the same for alpine based image. Where I can run ps command to get PID 1 process USER.
I didn't find any docs/hints around.

Answer 1

There is very cut version of ps in alpine image by default. It is busybox one:
/ # ps --help
BusyBox v1.27.2 (2017-12-12 10:41:50 GMT) multi-call binary.
Usage: ps [-o COL1,COL2=HEADER]
Show list of processes
-o COL1,COL2=HEADER Select columns for display
It can only show output with defined columns.
If you want use uncut ps, you need to install it first to alpine image:
/ # apk add --no-cache procps
fetch http://dl-cdn.alpinelinux.org/alpine/v3.7/main/x86_64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/v3.7/community/x86_64/APKINDEX.tar.gz
(1/6) Installing libintl (0.19.8.1-r1)
(2/6) Installing ncurses-terminfo-base (6.0_p20171125-r0)
(3/6) Installing ncurses-terminfo (6.0_p20171125-r0)
(4/6) Installing ncurses-libs (6.0_p20171125-r0)
(5/6) Installing libproc (3.3.12-r3)
(6/6) Installing procps (3.3.12-r3)
Executing busybox-1.27.2-r7.trigger
OK: 13 MiB in 17 packages
Now, you can use it you want:
/ # ps -p 1 -o user=
root