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put in a background loop

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edit approved Jul 16, 2018 at 16:41

simbo1905

$ cat run.sh
#!/bin/bashwhile true; do sleep 15 ; echo "background"; done &

while true; do sleep 30;12 ; echo "foreground"; done

Then it runs repeatedly showing:

foreground 
background 
foreground 
background

Now when I watch it I can see that it's staying up, in spite of the sleep 30 commands eventually "dying":

$ ps auxf
...
rootUSER     27913  0.1PID %CPU 4.6%MEM 726396 46888 ? VSZ   RSS TTY   Ssl  Jul13 STAT START 0:19 /usr/bin/dockerd-current --add-runtimeTIME docker-runc=/usr/libexec/docker/docker-runc-currentCOMMAND
root --default-runtime=docker-runc --exec-opt nativ
root     2791724  0.0  1.0 283900.1 10824 ?11828  2964 pts/1    Ss Ssl  Jul1316:00   0:06  \_00 /usr/bin/docker-containerd-currentbash
root -l unix:///var/run/docker/libcontainerd/docker-containerd.sock --metrics-interval=0 --start-timeou
root     2482358  0.0  0.3 255960  39121 ? 51712  3432 pts/1    SlR+   0216:2301   0:00   \_ ps auxf
root \_ /usr/bin/docker-containerd-shim-current 28c19c338e6e6177529cf989f42c7f14b17f1c705a61f5244d5350f0ab8f8364 /var/run/docker/libconta
root     248311  0.0  0.1  1168011692  13682572 pts/20    Ss+  0215:2358   0:00 /bin/bash /tmp/
root         \_5  0.0  0.1  11696  2272 pts/0    S+   15:58   0:00 /bin/bash /tmp/run.sh
root     25001   56  0.0  0.0   43604368   348636 pts/20    S+   0216:2501   0:00  \_ sleep 15
root        57  \_0.0  0.0   4368   664 pts/0    S+   16:01   0:00 sleep 3012

Now if we kill the background sleep 3015 like so:

$ kill 2500156

$ docker ps
...
rootUSER     27913  0.1PID %CPU 3.7%MEM 726396 38248 ? VSZ   RSS TTY   Ssl  Jul13 STAT START 0:19 /usr/bin/dockerd-current --add-runtimeTIME docker-runc=/usr/libexec/docker/docker-runc-currentCOMMAND
root --default-runtime=docker-runc --exec-opt nativ
root     2791724  0.0  1.0 283900.1 10768 ?11828  2964 pts/1    Ss Ssl  Jul1316:00   0:06  \_00 /usr/bin/docker-containerd-current -lbash
root unix:///var/run/docker/libcontainerd/docker-containerd.sock --metrics-interval=0 --start-timeou
root     2482360  0.0  0.3 255960  39121 ? 51712  3344 pts/1    SlR+   0216:2301   0:00   \_ ps auxf
root \_ /usr/bin/docker-containerd-shim-current 28c19c338e6e6177529cf989f42c7f14b17f1c705a61f5244d5350f0ab8f8364 /var/run/docker/libconta
root     248311  0.0  0.1  1168411692  13882572 pts/20    Ss+  0215:2358   0:00 /bin/bash /tmp/
root         5 \_ 0.0  0.1  11696  2272 pts/0    S+   15:58   0:00 /bin/bash /tmp/run.sh
root     25045   59  0.0  0.0   43604368   352636 pts/20    S+   0216:2601   0:00  \_ sleep 15
root        57  \_0.0  0.0   4368   664 pts/0    S+   16:01   0:00 sleep 3012

We can see that the while loop that's guarding our background sleep 3015 process has done its job and restarted another sleep 3015.

$ cat run.sh
#!/bin/bash

while true; do sleep 30; done

Now when I watch it I can see that it's staying up, in spite of the sleep 30 commands eventually "dying":

$ ps auxf
...
root     27913  0.1  4.6 726396 46888 ?        Ssl  Jul13   0:19 /usr/bin/dockerd-current --add-runtime docker-runc=/usr/libexec/docker/docker-runc-current --default-runtime=docker-runc --exec-opt nativ
root     27917  0.0  1.0 283900 10824 ?        Ssl  Jul13   0:06  \_ /usr/bin/docker-containerd-current -l unix:///var/run/docker/libcontainerd/docker-containerd.sock --metrics-interval=0 --start-timeou
root     24823  0.0  0.3 255960  3912 ?        Sl   02:23   0:00      \_ /usr/bin/docker-containerd-shim-current 28c19c338e6e6177529cf989f42c7f14b17f1c705a61f5244d5350f0ab8f8364 /var/run/docker/libconta
root     24831  0.0  0.1  11680  1368 pts/2    Ss+  02:23   0:00          \_ /bin/bash /tmp/run.sh
root     25001  0.0  0.0   4360   348 pts/2    S+   02:25   0:00              \_ sleep 30

Now if we kill sleep 30 like so:

$ kill 25001

$ docker ps
...
root     27913  0.1  3.7 726396 38248 ?        Ssl  Jul13   0:19 /usr/bin/dockerd-current --add-runtime docker-runc=/usr/libexec/docker/docker-runc-current --default-runtime=docker-runc --exec-opt nativ
root     27917  0.0  1.0 283900 10768 ?        Ssl  Jul13   0:06  \_ /usr/bin/docker-containerd-current -l unix:///var/run/docker/libcontainerd/docker-containerd.sock --metrics-interval=0 --start-timeou
root     24823  0.0  0.3 255960  3912 ?        Sl   02:23   0:00      \_ /usr/bin/docker-containerd-shim-current 28c19c338e6e6177529cf989f42c7f14b17f1c705a61f5244d5350f0ab8f8364 /var/run/docker/libconta
root     24831  0.0  0.1  11684  1388 pts/2    Ss+  02:23   0:00          \_ /bin/bash /tmp/run.sh
root     25045  0.0  0.0   4360   352 pts/2    S+   02:26   0:00              \_ sleep 30

We can see that the while loop that's guarding our sleep 30 process has done its job and restarted another sleep 30.

$ cat run.sh
while true; do sleep 15 ; echo "background"; done &

while true; do sleep 12 ; echo "foreground"; done

Then it runs repeatedly showing:

foreground 
background 
foreground 
background

Now when I watch it I can see that it's staying up, in spite of the sleep commands eventually "dying":

$ ps auxf
...
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root        24  0.0  0.1  11828  2964 pts/1    Ss   16:00   0:00 /bin/bash
root        58  0.0  0.1  51712  3432 pts/1    R+   16:01   0:00  \_ ps auxf
root         1  0.0  0.1  11692  2572 pts/0    Ss+  15:58   0:00 /bin/bash /tmp/
root         5  0.0  0.1  11696  2272 pts/0    S+   15:58   0:00 /bin/bash /tmp/
root        56  0.0  0.0   4368   636 pts/0    S+   16:01   0:00  \_ sleep 15
root        57  0.0  0.0   4368   664 pts/0    S+   16:01   0:00 sleep 12

Now if we kill the background sleep 15 like so:

$ kill 56

$ docker ps
...
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root        24  0.0  0.1  11828  2964 pts/1    Ss   16:00   0:00 /bin/bash
root        60  0.0  0.1  51712  3344 pts/1    R+   16:01   0:00  \_ ps auxf
root         1  0.0  0.1  11692  2572 pts/0    Ss+  15:58   0:00 /bin/bash /tmp/
root         5  0.0  0.1  11696  2272 pts/0    S+   15:58   0:00 /bin/bash /tmp/
root        59  0.0  0.0   4368   636 pts/0    S+   16:01   0:00  \_ sleep 15
root        57  0.0  0.0   4368   664 pts/0    S+   16:01   0:00 sleep 12

We can see that the while loop that's guarding our background sleep 15 process has done its job and restarted another sleep 15.

Source Link

answered Jul 14, 2018 at 6:30

slm ♦

379.8k
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Setup

I set up the following Dockerfile:

$ more Dockerfile
From centos
ADD run.sh /tmp/run.sh
RUN chmod +x /tmp/run.sh
ENTRYPOINT ["/tmp/run.sh"]

Setup a script, run.sh:

$ cat run.sh
#!/bin/bash

while true; do sleep 30; done

Built it:

$ docker build -t sleeper .
Sending build context to Docker daemon 7.791 MB
Step 1/4 : FROM centos
 ---> 49f7960eb7e4
Step 2/4 : ADD run.sh /tmp/run.sh
 ---> b4099de53780
Removing intermediate container 1ce8e3a1dac5
Step 3/4 : RUN chmod +x /tmp/run.sh
 ---> Running in e410429a6cba

 ---> 06789467e636
Removing intermediate container e410429a6cba
Step 4/4 : ENTRYPOINT /tmp/run.sh
 ---> Running in ad8b847b505f
 ---> a2415df63f99
Removing intermediate container ad8b847b505f
Successfully built a2415df63f99

Example

Then started it up:

$ docker run -dit sleeper
28c19c338e6e6177529cf989f42c7f14b17f1c705a61f5244d5350f0ab8f8364

Now when I watch it I can see that it's staying up, in spite of the sleep 30 commands eventually "dying":

$ docker ps
CONTAINER ID        IMAGE               COMMAND             CREATED              STATUS              PORTS               NAMES
28c19c338e6e        sleeper             "/tmp/run.sh"       About a minute ago   Up About a minute                       focused_lumiere

From above we can see that this container has been up in excess of 1 minute. Here's what the ps auxf looks like of the inside of the container:

$ ps auxf
...
root     27913  0.1  4.6 726396 46888 ?        Ssl  Jul13   0:19 /usr/bin/dockerd-current --add-runtime docker-runc=/usr/libexec/docker/docker-runc-current --default-runtime=docker-runc --exec-opt nativ
root     27917  0.0  1.0 283900 10824 ?        Ssl  Jul13   0:06  \_ /usr/bin/docker-containerd-current -l unix:///var/run/docker/libcontainerd/docker-containerd.sock --metrics-interval=0 --start-timeou
root     24823  0.0  0.3 255960  3912 ?        Sl   02:23   0:00      \_ /usr/bin/docker-containerd-shim-current 28c19c338e6e6177529cf989f42c7f14b17f1c705a61f5244d5350f0ab8f8364 /var/run/docker/libconta
root     24831  0.0  0.1  11680  1368 pts/2    Ss+  02:23   0:00          \_ /bin/bash /tmp/run.sh
root     25001  0.0  0.0   4360   348 pts/2    S+   02:25   0:00              \_ sleep 30

Now if we kill sleep 30 like so:

$ kill 25001

And run another docker ps:

$ docker ps
...
root     27913  0.1  3.7 726396 38248 ?        Ssl  Jul13   0:19 /usr/bin/dockerd-current --add-runtime docker-runc=/usr/libexec/docker/docker-runc-current --default-runtime=docker-runc --exec-opt nativ
root     27917  0.0  1.0 283900 10768 ?        Ssl  Jul13   0:06  \_ /usr/bin/docker-containerd-current -l unix:///var/run/docker/libcontainerd/docker-containerd.sock --metrics-interval=0 --start-timeou
root     24823  0.0  0.3 255960  3912 ?        Sl   02:23   0:00      \_ /usr/bin/docker-containerd-shim-current 28c19c338e6e6177529cf989f42c7f14b17f1c705a61f5244d5350f0ab8f8364 /var/run/docker/libconta
root     24831  0.0  0.1  11684  1388 pts/2    Ss+  02:23   0:00          \_ /bin/bash /tmp/run.sh
root     25045  0.0  0.0   4360   352 pts/2    S+   02:26   0:00              \_ sleep 30

We can see that the while loop that's guarding our sleep 30 process has done its job and restarted another sleep 30.