docker-alpine
docker-alpine copied to clipboard
alpinelinux
not all alpine can easily avoid pid=1
pid=1 in docker will cause many java tools exec exception, to avoid pid=1, we can easily put a command ahead , such as "set -ex;"
but we found only alpine3.7 alpine3.4 can avoid pid=1 by "set -ex;" we expect alpine3.x all support this .
the following test show alpine3.7/alpine3.4 pid=8, but other alpine pid=1
A simpler / more reliable solution would be to use Docker's --init flag which will add a simple PID 1 inside your container that reaps zombie processes for you.
I guess that's fair (IMO Kubernetes really should, but that's a different topic).
This is easily remedied via apk add --no-cache tini in your image, and then set it as your entrypoint via something like ENTRYPOINT ["/sbin/tini", "--"] (https://stackoverflow.com/a/50819443/433558).
(Tini is the exact solution Docker itself uses for implementing --init.)
@tianon google show several way to resolve the problem, but now the simple way is add "set -e" , we hope alpine will resolve it , alpine start with pid>1
just did quick debugging with strace, there was a slight difference in syscall between alpine 3.7 and 3.7+ on alpine 3.7 (or older version) the 'sleep' program would be running as a child process spawned by the syscall 'fork', so the pid was NOT 1, but on alpine 3.7+ this program was running inside the original process. see the strace syscalls snips below: on alpine 3.7
8366 03:12:37.855639 execve("/bin/sh", ["sh", "-c", "set -ex; sleep 370m"], [/* 6 vars */]) = 0 <0.000390>
...
# spawned a child process running "sleep" program
# pid 13 was the child process pid namespaced by the kernel
8366 03:12:37.865776 fork() = 13 <0.000420>
....
# pid 8367 was the child process pid in the root PID namespace
8367 03:12:37.868389 execve("/bin/sleep", ["sleep", "370m"], [/* 6 vars */]) = 0 <0.000552>
on alpine 3.8
9172 04:27:39.751880 execve("/bin/sh", ["sh", "-c", "set -ex; sleep 380m"], [/* 6 vars */]) = 0 <0.001089>
...
# the 'sleep' program running inside in the original process.
9172 04:27:39.763537 execve("/bin/sleep", ["sleep", "380m"], [/* 6 vars */]) = 0 <0.002119>
after deeper dig & debugging the behavior was intended, and related to the code commit in the busybox, @carlvine500, based on such code commit you can run 'sh' with the '-s' additional option, as following:
# the sh option '-s' can fork another process to execute your actual program, which the pid is NOT 1
# inside docker circumstance. see below:
$ docker run --name 3.10 -idt alpine:3.10 sh -cs "set -ex;sleep 310h"
6a1d ...
$ docker exec -it 3.10 ps aux
PID USER TIME COMMAND
1 root 0:00 sh -cs set -ex;sleep 310h
6 root 0:00 sleep 310h
7 root 0:00 ps aux
hope it helps, thanks
@inter169 thanks for your help ,it works in alpine3.10 but not woks in alpine3.14 .
