docker exec command doesn't return after completing execution - docker

Question

I started a docker container based on an image which has a file "run.sh" in it. Within a shell script, i use docker exec as shown below
docker exec <container-id> sh /test.sh
test.sh completes execution but docker exec does not return until i press ctrl+C. As a result, my shell script never ends. Any pointers to what might be causing this.

Answer 1

I could get it working with adding the -it parameters:
docker exec -it <container-id> sh /test.sh

Answer 2

Mine works like a charm with this command. Maybe you only forgot the path to the binary (/bin/sh)?
docker exec 7bd877d15c9b /bin/bash /test.sh
File location at
/test.sh
File Content:
#!/bin/bash
echo "Hi"
echo
echo "This works fine"
sleep 5
echo "5"
Output:
ArgonQQ#Terminal ~ docker exec 7bd877d15c9b /bin/bash /test.sh
Hi
This works fine
5
ArgonQQ#Terminal ~

Answer 3

My case is a script a.sh with content
like
php test.php &
if I execute it like
docker exec contianer1 a.sh
It also never returned.
After half a day googling and trying
changed a.sh to
php test.php >/tmp/test.log 2>&1 &
It works!
So it seems related with stdin/out/err.
>/tmp/test.log 2>&1
Please try.
And please note that my test.php is a dead loop script that monitors a specified process, if the process is down, it will restart it. So test.php will never exit.

Answer 4

As described here, this "hanging" behavior occurs when you have processes that keep stdout or stderr open.
To prevent this from happening, each long-running process should:
be executed in the background, and
close both stdout and stderr or redirect them to files or /dev/null.
I would therefore make sure that any processes already running in the container, as well as the script passed to docker exec, conform to the above.

Answer 5

OK, I got it.
docker stop a590382c2943
docker start a590382c2943
then will be ok.
docker exec -ti a590382c2943 echo "5"
will return immediately, while add -it or not, no use
actually, in my program, the deamon has the std input and std output, std err. so I change my python deamon like following, things work like a charm:
if __name__ == '__main__':
# do the UNIX double-fork magic, see Stevens' "Advanced
# Programming in the UNIX Environment" for details (ISBN 0201563177)
try:
pid = os.fork()
if pid > 0:
# exit first parent
os._exit(0)
except OSError, e:
print "fork #1 failed: %d (%s)" % (e.errno, e.strerror)
os._exit(0)
# decouple from parent environment
#os.chdir("/")
os.setsid()
os.umask(0)
#std in out err, redirect
si = file('/dev/null', 'r')
so = file('/dev/null', 'a+')
se = file('/dev/null', 'a+', 0)
os.dup2(si.fileno(), sys.stdin.fileno())
os.dup2(so.fileno(), sys.stdout.fileno())
os.dup2(se.fileno(), sys.stderr.fileno())
# do second fork
while(True):
try:
pid = os.fork()
if pid == 0:
serve()
if pid > 0:
print "Server PID %d, Daemon PID: %d" % (pid, os.getpid())
os.wait()
time.sleep(3)
except OSError, e:
#print "fork #2 failed: %d (%s)" % (e.errno, e.strerror)
os._exit(0)