I'm trying to run background tasks in Codebuild using the nohup command as described in the document (https://docs.aws.amazon.com/codebuild/latest/userguide/build-env-ref-background-tasks.html)
Below is the buildspec I'm using
version: 0.2
phases:
build:
commands:
- nohup sleep 30 & echo $! > pidfile
- wait $(cat pidfile)
I get an error for this as below
[Container] 2021/08/25 06:04:40 Running command wait $(cat pidfile)
/codebuild/output/tmp/script.sh: line 4: wait: pid 207 is not a child of this shell
[Container] 2021/08/25 06:04:40 Command did not exit successfully wait $(cat pidfile) exit status 127
[Container] 2021/08/25 06:04:40 Phase complete: BUILD State: FAILED
I do not understand why the wait command i being executed in a different shell. Is there any way how I can make this execute in the same shell or am I doing it wrong?
I experienced the same, sometimes wait doesn't work in CodeBuild.
I found an answer here that might explain the issue.
There can be workarounds to replace wait:
poll the PID until it exists, e.g.: while [ -e /proc/$PID ]; do sleep 1; done (from here), or you can also use ps --pid $PID > /dev/null or kill -0 $PID 2>/dev/null or some other solutions to determine whether the background process finished
copy the stdout file descriptor of the command to a custom one, and read from that until it is closed:
exec 3< <(sleep 3 2>&1)
...
cat <&3 # print the output of the background process and will wait until it exits
A big limitation of these is that the exit code of the background process is unknown (wait would return with that). You have to save it somewhere if you need it.
Related
This question already has answers here:
Timeout a command in bash without unnecessary delay
(24 answers)
Closed 2 years ago.
On stackoverflow there are many solutions - how to close script by timeout or close script if there is an error.
But how to have both approaches together?
If during execution of the script there is an error - close script.
If timeout is out - close script.
I have following code:
#!/usr/bin/env bash
set -e
finish_time=$1
echo "finish_time=" ${finish_time}
(./execute_something.sh) & pid=$!
sleep ${finish_time}
kill $pid
But if there is an error while execution - script still waits, when timeout would be out.
First, I won't use set -e.
You'll explicitly wait on the job you want; the exit status of wait will be the exit status of the job itself.
echo "finish_time = $1"
./execute_something.sh & pid=$!
sleep "$1" & sleep_pid=$!
wait -n # Waits for either the sleep or the script to finish
rv=$?
if kill -0 $pid; then
# Script still running, kill it
# and exit
kill -s ALRM $pid
wait $pid # exit status will indicte it was killed by SIGALRM
exit
else
# Script exited before sleep
kill $sleep_pid
exit $rv
fi
There is a slight race condition here; it goes as follows:
wait -n returns after sleep exits, indicating the script will exit on its own
The script exits before we can check if it is still running
As a result, we assume it actually exited before sleep.
But that just means we'll create a script that ran slightly over the threshold as finishing on time. That's probably not a distinction you care about.
Ideally, wait would set some shell parameter that indicates which process caused it to return.
I am trying to use daemon on Ubuntu, but I am not sure how to use it even after reading the man page.
I have the following testing script foo.sh
#!/bin/bash
while true; do
echo 'hi' >> ~/hihihi
sleep 10
done
Then I tried this command but nothing happened:
daemon --name="foo" -b ~/daemon.out -l ~/daemon.err -v -- foo.sh
The file hihihi was not updated, and I found this in the errlog:
20161221 12:12:36 foo: client (pid 176193) exited with 1 status
How could I use the daemon command properly?
AFAIK, most daemon or deamonize programs change the current dir to root as part of the daemonization process. That means that you must give the full path of the command:
daemon --name="foo" -b ~/daemon.out -l ~/daemon.err -v -- /path/to/foo.sh
If it still did not work, you could try to specify a shell:
daemon --name="foo" -b ~/daemon.out -l ~/daemon.err -v -- /bin/bash -c /path/to/foo.sh
It is not necessary to use daemon command in bash. You can daemonize your script manually. For example:
#!/bin/bash
# At first you have to redirect stdout and stderr to /dev/null
exec >/dev/null
exec 2>/dev/null
# Fork and go to background
(
while true; do
echo 'hi' >> ~/hihihi
sleep 10
done
)&
# Parent process finished but child still working
How can you suppress the Terminated message that comes up after you kill a
process in a bash script?
I tried set +bm, but that doesn't work.
I know another solution involves calling exec 2> /dev/null, but is that
reliable? How do I reset it back so that I can continue to see stderr?
In order to silence the message, you must be redirecting stderr at the time the message is generated. Because the kill command sends a signal and doesn't wait for the target process to respond, redirecting stderr of the kill command does you no good. The bash builtin wait was made specifically for this purpose.
Here is very simple example that kills the most recent background command. (Learn more about $! here.)
kill $!
wait $! 2>/dev/null
Because both kill and wait accept multiple pids, you can also do batch kills. Here is an example that kills all background processes (of the current process/script of course).
kill $(jobs -rp)
wait $(jobs -rp) 2>/dev/null
I was led here from bash: silently kill background function process.
The short answer is that you can't. Bash always prints the status of foreground jobs. The monitoring flag only applies for background jobs, and only for interactive shells, not scripts.
see notify_of_job_status() in jobs.c.
As you say, you can redirect so standard error is pointing to /dev/null but then you miss any other error messages. You can make it temporary by doing the redirection in a subshell which runs the script. This leaves the original environment alone.
(script 2> /dev/null)
which will lose all error messages, but just from that script, not from anything else run in that shell.
You can save and restore standard error, by redirecting a new filedescriptor to point there:
exec 3>&2 # 3 is now a copy of 2
exec 2> /dev/null # 2 now points to /dev/null
script # run script with redirected stderr
exec 2>&3 # restore stderr to saved
exec 3>&- # close saved version
But I wouldn't recommend this -- the only upside from the first one is that it saves a sub-shell invocation, while being more complicated and, possibly even altering the behavior of the script, if the script alters file descriptors.
EDIT:
For more appropriate answer check answer given by Mark Edgar
Solution: use SIGINT (works only in non-interactive shells)
Demo:
cat > silent.sh <<"EOF"
sleep 100 &
kill -INT $!
sleep 1
EOF
sh silent.sh
http://thread.gmane.org/gmane.comp.shells.bash.bugs/15798
Maybe detach the process from the current shell process by calling disown?
The Terminated is logged by the default signal handler of bash 3.x and 4.x. Just trap the TERM signal at the very first of child process:
#!/bin/sh
## assume script name is test.sh
foo() {
trap 'exit 0' TERM ## here is the key
while true; do sleep 1; done
}
echo before child
ps aux | grep 'test\.s[h]\|slee[p]'
foo &
pid=$!
sleep 1 # wait trap is done
echo before kill
ps aux | grep 'test\.s[h]\|slee[p]'
kill $pid ## no need to redirect stdin/stderr
sleep 1 # wait kill is done
echo after kill
ps aux | grep 'test\.s[h]\|slee[p]'
Is this what we are all looking for?
Not wanted:
$ sleep 3 &
[1] 234
<pressing enter a few times....>
$
$
[1]+ Done sleep 3
$
Wanted:
$ (set +m; sleep 3 &)
<again, pressing enter several times....>
$
$
$
$
$
As you can see, no job end message. Works for me in bash scripts as well, also for killed background processes.
'set +m' disables job control (see 'help set') for the current shell. So if you enter your command in a subshell (as done here in brackets) you will not influence the job control settings of the current shell. Only disadvantage is that you need to get the pid of your background process back to the current shell if you want to check whether it has terminated, or evaluate the return code.
This also works for killall (for those who prefer it):
killall -s SIGINT (yourprogram)
suppresses the message... I was running mpg123 in background mode.
It could only silently be killed by sending a ctrl-c (SIGINT) instead of a SIGTERM (default).
disown did exactly the right thing for me -- the exec 3>&2 is risky for a lot of reasons -- set +bm didn't seem to work inside a script, only at the command prompt
Had success with adding 'jobs 2>&1 >/dev/null' to the script, not certain if it will help anyone else's script, but here is a sample.
while true; do echo $RANDOM; done | while read line
do
echo Random is $line the last jobid is $(jobs -lp)
jobs 2>&1 >/dev/null
sleep 3
done
Another way to disable job notifications is to place your command to be backgrounded in a sh -c 'cmd &' construct.
#!/bin/bash
# ...
pid="`sh -c 'sleep 30 & echo ${!}' | head -1`"
kill "$pid"
# ...
# or put several cmds in sh -c '...' construct
sh -c '
sleep 30 &
pid="${!}"
sleep 5
kill "${pid}"
'
I found that putting the kill command in a function and then backgrounding the function suppresses the termination output
function killCmd() {
kill $1
}
killCmd $somePID &
Simple:
{ kill $! } 2>/dev/null
Advantage? can use any signal
ex:
{ kill -9 $PID } 2>/dev/null
edit
For future readers. The root of this problem really came down to running the function in an interactive shell vs. putting it in a separate script.
Also, there are many things that could be improved in the code I originally posted. Please see comments for things that could/should have been done better.
/edit
I have a bash function intended to rerun a process in the background when files in a directory change (think like Grunt, but for general purposes). The script functions as desired while running:
The subprocess is correctly started (including any children)
On file change, the sub is killed (including children) and started again
However, on exit (ctrl-c) none of the processes are killed. Additionally, pressing ctrl-c a second time will kill the current terminal session. I'm assuming this is a problem with my trap, but have been unable to identify a reason for the issue.
Here is the code of rerun.sh
#!/bin/bash
# rerun.sh
_kill_children() {
isTop=$1
curPid=$2
# Get pids of children
children=`ps -o pid --no-headers --ppid ${curPid}`
for child in $children
do
# Call this function to get grandchildren as well
_kill_children 0 $child
done
# Parent calls this with 1, all other with 0 so only children are killed
if [[ $isTop -eq 0 ]]; then
kill -9 $curPid 2> /dev/null
fi
}
rerun() {
trap " _kill_children 1 $$; exit 0" SIGINT SIGTERM
FORMAT=$(echo -e "\033[1;33m%w%f\033[0m written")
#Command that should be repeatedly run is passed as args
args=$#
$args &
#When a file changes in the directory, rerun the process
while inotifywait -qre close_write --format "$FORMAT" .
do
#Kill current bg proc and it's children
_kill_children 1 $$
$args & #Rerun the proc
done
}
#This is sourced in my bash profile so I can run it any time
To test this, create a pair of executable files parent.sh and child.sh as follows:
#!/bin/bash
#parent.sh
./child.sh
#!/bin/bash
#child.sh
sleep 86400
Then source the rerun.sh file and run rerun ./parent.sh. In another terminal window I watch "ps -ef | grep pts/4" to see all processes for the rerun (in this example on pts/4). Touching a file in the directory triggers a restart of parent.sh and children. [ctrl-c] exits, but leaves the pids running. [ctrl-c] again kills bash and all other processes on pts/4.
Desired behavior: on [ctrl-c], kill children and exit to shell normally. Help?
--
Code sources:
Inotify idea from: https://exyr.org/2011/inotify-run/
Kill children from: http://riccomini.name/posts/linux/2012-09-25-kill-subprocesses-linux-bash/
This isn't a good practice to follow in the first place. Track your children explicitly:
children=( )
foo & children+=( "$!" )
...then, you can kill or wait for them explicitly, referring to "${children[#]}" for the list. If you want to get grandchildren as well, this is a good user for fuser -k and a lockfile:
lockfile_name="$(mktemp /tmp/lockfile.XXXXXX)" # change appropriately
trap 'rm -f "$lockfile_name"' 0
exec 3>"$lockfile_name" # open lockfile on FD 3
kill_children() {
# close our own handle on the lockfile
exec 3>&-
# kill everything that still has it open (our children and their children)
fuser -k "$lockfile_name" >/dev/null
# ...then open it again.
exec 3>"$lockfile_name"
}
rerun() {
trap 'kill_children; exit 0' SIGINT SIGTERM
printf -v format '%b' "\033[1;33m%w%f\033[0m written"
"$#" &
#When a file changes in the directory, rerun the process
while inotifywait -qre close_write --format "$format" .; do
kill_children
"$#" &
done
}
I have a bash script that launches a child process that crashes (actually, hangs) from time to time and with no apparent reason (closed source, so there isn't much I can do about it). As a result, I would like to be able to launch this process for a given amount of time, and kill it if it did not return successfully after a given amount of time.
Is there a simple and robust way to achieve that using bash?
P.S.: tell me if this question is better suited to serverfault or superuser.
(As seen in:
BASH FAQ entry #68: "How do I run a command, and have it abort (timeout) after N seconds?")
If you don't mind downloading something, use timeout (sudo apt-get install timeout) and use it like: (most Systems have it already installed otherwise use sudo apt-get install coreutils)
timeout 10 ping www.goooooogle.com
If you don't want to download something, do what timeout does internally:
( cmdpid=$BASHPID; (sleep 10; kill $cmdpid) & exec ping www.goooooogle.com )
In case that you want to do a timeout for longer bash code, use the second option as such:
( cmdpid=$BASHPID;
(sleep 10; kill $cmdpid) \
& while ! ping -w 1 www.goooooogle.com
do
echo crap;
done )
# Spawn a child process:
(dosmth) & pid=$!
# in the background, sleep for 10 secs then kill that process
(sleep 10 && kill -9 $pid) &
or to get the exit codes as well:
# Spawn a child process:
(dosmth) & pid=$!
# in the background, sleep for 10 secs then kill that process
(sleep 10 && kill -9 $pid) & waiter=$!
# wait on our worker process and return the exitcode
exitcode=$(wait $pid && echo $?)
# kill the waiter subshell, if it still runs
kill -9 $waiter 2>/dev/null
# 0 if we killed the waiter, cause that means the process finished before the waiter
finished_gracefully=$?
sleep 999&
t=$!
sleep 10
kill $t
I also had this question and found two more things very useful:
The SECONDS variable in bash.
The command "pgrep".
So I use something like this on the command line (OSX 10.9):
ping www.goooooogle.com & PING_PID=$(pgrep 'ping'); SECONDS=0; while pgrep -q 'ping'; do sleep 0.2; if [ $SECONDS = 10 ]; then kill $PING_PID; fi; done
As this is a loop I included a "sleep 0.2" to keep the CPU cool. ;-)
(BTW: ping is a bad example anyway, you just would use the built-in "-t" (timeout) option.)
Assuming you have (or can easily make) a pid file for tracking the child's pid, you could then create a script that checks the modtime of the pid file and kills/respawns the process as needed. Then just put the script in crontab to run at approximately the period you need.
Let me know if you need more details. If that doesn't sound like it'd suit your needs, what about upstart?
One way is to run the program in a subshell, and communicate with the subshell through a named pipe with the read command. This way you can check the exit status of the process being run and communicate this back through the pipe.
Here's an example of timing out the yes command after 3 seconds. It gets the PID of the process using pgrep (possibly only works on Linux). There is also some problem with using a pipe in that a process opening a pipe for read will hang until it is also opened for write, and vice versa. So to prevent the read command hanging, I've "wedged" open the pipe for read with a background subshell. (Another way to prevent a freeze to open the pipe read-write, i.e. read -t 5 <>finished.pipe - however, that also may not work except with Linux.)
rm -f finished.pipe
mkfifo finished.pipe
{ yes >/dev/null; echo finished >finished.pipe ; } &
SUBSHELL=$!
# Get command PID
while : ; do
PID=$( pgrep -P $SUBSHELL yes )
test "$PID" = "" || break
sleep 1
done
# Open pipe for writing
{ exec 4>finished.pipe ; while : ; do sleep 1000; done } &
read -t 3 FINISHED <finished.pipe
if [ "$FINISHED" = finished ] ; then
echo 'Subprocess finished'
else
echo 'Subprocess timed out'
kill $PID
fi
rm finished.pipe
Here's an attempt which tries to avoid killing a process after it has already exited, which reduces the chance of killing another process with the same process ID (although it's probably impossible to avoid this kind of error completely).
run_with_timeout ()
{
t=$1
shift
echo "running \"$*\" with timeout $t"
(
# first, run process in background
(exec sh -c "$*") &
pid=$!
echo $pid
# the timeout shell
(sleep $t ; echo timeout) &
waiter=$!
echo $waiter
# finally, allow process to end naturally
wait $pid
echo $?
) \
| (read pid
read waiter
if test $waiter != timeout ; then
read status
else
status=timeout
fi
# if we timed out, kill the process
if test $status = timeout ; then
kill $pid
exit 99
else
# if the program exited normally, kill the waiting shell
kill $waiter
exit $status
fi
)
}
Use like run_with_timeout 3 sleep 10000, which runs sleep 10000 but ends it after 3 seconds.
This is like other answers which use a background timeout process to kill the child process after a delay. I think this is almost the same as Dan's extended answer (https://stackoverflow.com/a/5161274/1351983), except the timeout shell will not be killed if it has already ended.
After this program has ended, there will still be a few lingering "sleep" processes running, but they should be harmless.
This may be a better solution than my other answer because it does not use the non-portable shell feature read -t and does not use pgrep.
Here's the third answer I've submitted here. This one handles signal interrupts and cleans up background processes when SIGINT is received. It uses the $BASHPID and exec trick used in the top answer to get the PID of a process (in this case $$ in a sh invocation). It uses a FIFO to communicate with a subshell that is responsible for killing and cleanup. (This is like the pipe in my second answer, but having a named pipe means that the signal handler can write into it too.)
run_with_timeout ()
{
t=$1 ; shift
trap cleanup 2
F=$$.fifo ; rm -f $F ; mkfifo $F
# first, run main process in background
"$#" & pid=$!
# sleeper process to time out
( sh -c "echo \$\$ >$F ; exec sleep $t" ; echo timeout >$F ) &
read sleeper <$F
# control shell. read from fifo.
# final input is "finished". after that
# we clean up. we can get a timeout or a
# signal first.
( exec 0<$F
while : ; do
read input
case $input in
finished)
test $sleeper != 0 && kill $sleeper
rm -f $F
exit 0
;;
timeout)
test $pid != 0 && kill $pid
sleeper=0
;;
signal)
test $pid != 0 && kill $pid
;;
esac
done
) &
# wait for process to end
wait $pid
status=$?
echo finished >$F
return $status
}
cleanup ()
{
echo signal >$$.fifo
}
I've tried to avoid race conditions as far as I can. However, one source of error I couldn't remove is when the process ends near the same time as the timeout. For example, run_with_timeout 2 sleep 2 or run_with_timeout 0 sleep 0. For me, the latter gives an error:
timeout.sh: line 250: kill: (23248) - No such process
as it is trying to kill a process that has already exited by itself.
#Kill command after 10 seconds
timeout 10 command
#If you don't have timeout installed, this is almost the same:
sh -c '(sleep 10; kill "$$") & command'
#The same as above, with muted duplicate messages:
sh -c '(sleep 10; kill "$$" 2>/dev/null) & command'