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Last active March 27, 2020 02:50
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Right use entrypoint and cmd in Dockerfile
Raw
Dockerfile
FROM alpine:3.11
COPY entrypoint.sh /entrypoint.sh
COPY process.sh /process.sh
RUN chmod +x /entrypoint.sh /process.sh
ENTRYPOINT ["/entrypoint.sh"]
CMD ["/process.sh"]
Raw
entrypoint.sh
#!/bin/sh
set -e
trap handle_trap INT
function handle_trap() {
echo "trapped in entrypoint.sh"
exit 1
}
echo "begin entrypoint.sh"
exec "$@"
# the following line will be not executed.
echo "end entrypoint.sh"
Raw
output
$ docker build -t test .
$ docker --rm run test
begin entrypoint.sh
begin process.sh
Mem: 711664K used, 1055120K free, 16888K shrd, 2108K buff, 403816K cached
CPU: 0% usr 0% sys 0% nic 100% idle 0% io 0% irq 0% sirq
Load average: 0.03 0.05 0.06 1/173 6
PID PPID USER STAT VSZ %VSZ CPU %CPU COMMAND
6 1 root R 1580 0% 0 0% top
1 0 root S 1572 0% 0 0% {process.sh} /bin/sh /process.sh
waiting for process(pid=$PID)
trapped in process.sh
Raw
process.sh
#!/bin/sh
set -e
trap handle_trap INT
function handle_trap() {
echo "trapped in process.sh"
kill -TERM $PID
wait $PID
exit 1
}
echo "begin process.sh"
# make a child process of process.sh
top &
PID=$!
echo "waiting for process(pid=$PID)"
wait $PID
# the following line will be not executed.
echo "end process.sh"
@odg0318
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odg0318 commented Feb 13, 2020 •
edited
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Description

List type of ENTRYPOINT is recommended in Dockerfile.
An example like above can be received INT signal from docker command.

Flow

  1. /entrypoint.sh /process.sh is executed in a container.
  2. /process.sh is executed by exec command with the same pid as /entrypoint.sh, which makes /process.sh receive kill signals.
  3. top is executed on the background and /process.sh waits for its exiting.
  4. Container receives INT kill signal by ctrl+c, which is trapped in /process.sh.
  5. handle_trap function finally kills top process and /process.sh also exits.

References

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