I have been trying to figure this one out for a while. I am trying to automate a few things. I only have rights to edit the scripts I write. I am currently using my script to call another script that I cannot edit, let's call it script.sh
I have tried:
if [[ -n $PASS ]]; then
su -c 'echo "$PASS" | ./script.sh' &
wait $!
else
./script.sh &
wait $!
fi
if [[ -n $PASS ]]; then
echo "$PASS" | ./script.sh &
wait $!
else
./script.sh &
wait $!
fi
if [[ -n $PASS ]]; then
./script.sh <<< $PASS &
wait $!
else
./script.sh &
wait $!
fi
This calls a script I cannot edit:
#!/bin/bash
echo "foo: "
read PASSWORD
echo
echo "foo"
...
if [ ! -f ./config.ini ]; then
./script2.sh ./config.ini
fi
My issue it that script.sh then calls another script, let's say script2.sh, that cats out a config.ini file to be used later in the process. Script2.sh fails to create config.ini correctly. Specifically the command user=$(/usr/bin/who am i | cut -d ' ' -f1) fails to set the variable.
So, 3 scripts deep one command fails. But it works if run manually or if I don't echo $PASS and enter it manually. Any ideas would be greatly appreciated.
I know I can run my bash script in the background by using bash script.sh & disown or alternatively, by using nohup. However, I want to run my script in the background by default, so when I run bash script.sh or after making it executable, by running ./script.sh it should run in the background by default. How can I achieve this?
Self-contained solution:
#!/bin/sh
# Re-spawn as a background process, if we haven't already.
if [[ "$1" != "-n" ]]; then
nohup "$0" -n &
exit $?
fi
# Rest of the script follows. This is just an example.
for i in {0..10}; do
sleep 2
echo $i
done
The if statement checks if the -n flag has been passed. If not, it calls itself with nohup (to disassociate the calling terminal so closing it doesn't close the script) and & (to put the process in the background and return to the prompt). The parent then exits to leave the background version to run. The background version is explicitly called with the -n flag, so wont cause an infinite loop (which is hell to debug!).
The for loop is just an example. Use tail -f nohup.out to see the script's progress.
Note that I pieced this answer together with this and this but neither were succinct or complete enough to be a duplicate.
Simply write a wrapper that calls your actual script with nohup actualScript.sh &.
Wrapper script wrapper.sh
#! /bin/bash
nohup ./actualScript.sh &
Actual script in actualScript.sh
#! /bin/bash
for i in {0..10}
do
sleep 10 #script is running, test with ps -eaf|grep actualScript
echo $i
done
tail -f 10 nohup.out
0
1
2
3
4
...
Adding to Heath Raftery's answer, what worked for me is a variation of what he suggested such as this:
if [[ "$1" != "-n" ]]; then
$0 -n & disown
exit $?
fi
I have a function in a bash script that runs indefinitely in background and that shall be terminated by running again the same script. It is a sort of switch, when I invoke this script it starts or kills the function if already running. To do this I use a PID file:
#!/bin/bash
background_function() {
...
}
if [[ ! -s myscript.pid ]]
then
background_function &
echo $! > myscript.pid
else
kill $(cat myscript.pid) && rm myscript.pid
fi
Now, I would like to avoid multiple instances running and race conditions. I tried to use flock and I rewrote the above code in this way:
#!/bin/bash
background_function() {
...
}
exec 200>myscript.pid
if flock -n 200
then
background_function &
echo $! > myscript.pid
else
kill $(cat myscript.pid) && rm myscript.pid
fi
In doing so, however, I have a lock on the pid file but every time I launch the script again the pid file is rewritten by exec 200>myscript.pid and therefore I am unable to retrieve the PID of the already running instance and kill it.
What can I do? Should I use two different files, a pid file and a lock file? Or would it be better to implement other lock mechanisms by using mkdir and touch? Thanks.
If an echo $$ is atomic enough for you, you could use:
echo $$ >> lock.pid
lockedby=`head -1 lock.pid`
if [ $$ != $lockedby ] ; then
kill -9 $lockedby
echo $$ > lock.pid
echo "Murdered $lockedby because it had the lock"
fi
# do things in the script
rm lock.pid
I currently use the technique described in How do I write a bash script to restart a process if it dies? by lhunath in order to restart a dead process.
until myserver; do
echo "Server 'myserver' crashed with exit code $?. Respawning.." >&2
sleep 1
done
But rather than just invoking the process myserver, I would like to invoke such a thing:
myserver 2>&1 | /usr/bin/logger -p local0.info &
How to use the first technique with a process with pipe?
The until loop itself can be piped into logger:
until myserver 2>&1; do
echo "..."
sleep 1
done | /usr/bin/logger -p local0.info &
since myserver inherits its standard output and error from the loop (which inherits from the shell).
You can use the PIPESTATUS variable to get the exit code from a specific command in a pipeline:
while :; do
myserver 2>&1 | /usr/bin/logger -p local0.info
if [[ ${PIPESTATUS[0]} != 0 ]]
then echo "Server 'myserver' crashed with exit code ${PIPESTATUS[0]}. Respawning.." >&2
sleep 1
else break
fi
done
I'm wondering if there is a better way to make a daemon that waits for something using only sh than:
#! /bin/sh
trap processUserSig SIGUSR1
processUserSig() {
echo "doing stuff"
}
while true; do
sleep 1000
done
In particular, I'm wondering if there's any way to get rid of the loop and still have the thing listen for the signals.
Just backgrounding your script (./myscript &) will not daemonize it. See http://www.faqs.org/faqs/unix-faq/programmer/faq/, section 1.7, which describes what's necessary to become a daemon. You must disconnect it from the terminal so that SIGHUP does not kill it. You can take a shortcut to make a script appear to act like a daemon;
nohup ./myscript 0<&- &>/dev/null &
will do the job. Or, to capture both stderr and stdout to a file:
nohup ./myscript 0<&- &> my.admin.log.file &
Redirection explained (see bash redirection)
0<&- closes stdin
&> file sends stdout and stderr to a file
However, there may be further important aspects that you need to consider. For example:
You will still have a file descriptor open to the script, which means that the directory it's mounted in would be unmountable. To be a true daemon you should chdir("/") (or cd / inside your script), and fork so that the parent exits, and thus the original descriptor is closed.
Perhaps run umask 0. You may not want to depend on the umask of the caller of the daemon.
For an example of a script that takes all of these aspects into account, see Mike S' answer.
Some of the top-upvoted answers here are missing some important parts of what makes a daemon a daemon, as opposed to just a background process, or a background process detached from a shell.
This http://www.faqs.org/faqs/unix-faq/programmer/faq/ describes what is necessary to be a daemon. And this Run bash script as daemon implements the setsid, though it misses the chdir to root.
The original poster's question was actually more specific than "How do I create a daemon process using bash?", but since the subject and answers discuss daemonizing shell scripts generally, I think it's important to point it out (for interlopers like me looking into the fine details of creating a daemon).
Here's my rendition of a shell script that would behave according to the FAQ. Set DEBUG to true to see pretty output (but it also exits immediately rather than looping endlessly):
#!/bin/bash
DEBUG=false
# This part is for fun, if you consider shell scripts fun- and I do.
trap process_USR1 SIGUSR1
process_USR1() {
echo 'Got signal USR1'
echo 'Did you notice that the signal was acted upon only after the sleep was done'
echo 'in the while loop? Interesting, yes? Yes.'
exit 0
}
# End of fun. Now on to the business end of things.
print_debug() {
whatiam="$1"; tty="$2"
[[ "$tty" != "not a tty" ]] && {
echo "" >$tty
echo "$whatiam, PID $$" >$tty
ps -o pid,sess,pgid -p $$ >$tty
tty >$tty
}
}
me_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
me_FILE=$(basename $0)
cd /
#### CHILD HERE --------------------------------------------------------------------->
if [ "$1" = "child" ] ; then # 2. We are the child. We need to fork again.
shift; tty="$1"; shift
$DEBUG && print_debug "*** CHILD, NEW SESSION, NEW PGID" "$tty"
umask 0
$me_DIR/$me_FILE XXrefork_daemonXX "$tty" "$#" </dev/null >/dev/null 2>/dev/null &
$DEBUG && [[ "$tty" != "not a tty" ]] && echo "CHILD OUT" >$tty
exit 0
fi
##### ENTRY POINT HERE -------------------------------------------------------------->
if [ "$1" != "XXrefork_daemonXX" ] ; then # 1. This is where the original call starts.
tty=$(tty)
$DEBUG && print_debug "*** PARENT" "$tty"
setsid $me_DIR/$me_FILE child "$tty" "$#" &
$DEBUG && [[ "$tty" != "not a tty" ]] && echo "PARENT OUT" >$tty
exit 0
fi
##### RUNS AFTER CHILD FORKS (actually, on Linux, clone()s. See strace -------------->
# 3. We have been reforked. Go to work.
exec >/tmp/outfile
exec 2>/tmp/errfile
exec 0</dev/null
shift; tty="$1"; shift
$DEBUG && print_debug "*** DAEMON" "$tty"
# The real stuff goes here. To exit, see fun (above)
$DEBUG && [[ "$tty" != "not a tty" ]] && echo NOT A REAL DAEMON. NOT RUNNING WHILE LOOP. >$tty
$DEBUG || {
while true; do
echo "Change this loop, so this silly no-op goes away." >/dev/null
echo "Do something useful with your life, young padawan." >/dev/null
sleep 10
done
}
$DEBUG && [[ "$tty" != "not a tty" ]] && sleep 3 && echo "DAEMON OUT" >$tty
exit # This may never run. Why is it here then? It's pretty.
# Kind of like, "The End" at the end of a movie that you
# already know is over. It's always nice.
Output looks like this when DEBUG is set to true. Notice how the session and process group ID (SESS, PGID) numbers change:
<shell_prompt>$ bash blahd
*** PARENT, PID 5180
PID SESS PGID
5180 1708 5180
/dev/pts/6
PARENT OUT
<shell_prompt>$
*** CHILD, NEW SESSION, NEW PGID, PID 5188
PID SESS PGID
5188 5188 5188
not a tty
CHILD OUT
*** DAEMON, PID 5198
PID SESS PGID
5198 5188 5188
not a tty
NOT A REAL DAEMON. NOT RUNNING WHILE LOOP.
DAEMON OUT
# double background your script to have it detach from the tty
# cf. http://www.linux-mag.com/id/5981
(./program.sh &) &
Use your system's daemon facility, such as start-stop-daemon.
Otherwise, yes, there has to be a loop somewhere.
$ ( cd /; umask 0; setsid your_script.sh </dev/null &>/dev/null & ) &
It really depends on what is the binary itself going to do.
For example I want to create some listener.
The starting Daemon is simple task :
lis_deamon :
#!/bin/bash
# We will start the listener as Deamon process
#
LISTENER_BIN=/tmp/deamon_test/listener
test -x $LISTENER_BIN || exit 5
PIDFILE=/tmp/deamon_test/listener.pid
case "$1" in
start)
echo -n "Starting Listener Deamon .... "
startproc -f -p $PIDFILE $LISTENER_BIN
echo "running"
;;
*)
echo "Usage: $0 start"
exit 1
;;
esac
this is how we start the daemon (common way for all /etc/init.d/ staff)
now as for the listener it self,
It must be some kind of loop/alert or else that will trigger the script
to do what u want. For example if u want your script to sleep 10 min
and wake up and ask you how you are doing u will do this with the
while true ; do sleep 600 ; echo "How are u ? " ; done
Here is the simple listener that u can do that will listen for your
commands from remote machine and execute them on local :
listener :
#!/bin/bash
# Starting listener on some port
# we will run it as deamon and we will send commands to it.
#
IP=$(hostname --ip-address)
PORT=1024
FILE=/tmp/backpipe
count=0
while [ -a $FILE ] ; do #If file exis I assume that it used by other program
FILE=$FILE.$count
count=$(($count + 1))
done
# Now we know that such file do not exist,
# U can write down in deamon it self the remove for those files
# or in different part of program
mknod $FILE p
while true ; do
netcat -l -s $IP -p $PORT < $FILE |/bin/bash > $FILE
done
rm $FILE
So to start UP it : /tmp/deamon_test/listener start
and to send commands from shell (or wrap it to script) :
test_host#netcat 10.184.200.22 1024
uptime
20:01pm up 21 days 5:10, 44 users, load average: 0.62, 0.61, 0.60
date
Tue Jan 28 20:02:00 IST 2014
punt! (Cntrl+C)
Hope this will help.
Have a look at the daemon tool from the libslack package:
http://ingvar.blog.linpro.no/2009/05/18/todays-sysadmin-tip-using-libslack-daemon-to-daemonize-a-script/
On Mac OS X use a launchd script for shell daemon.
If I had a script.sh and i wanted to execute it from bash and leave it running even when I want to close my bash session then I would combine nohup and & at the end.
example: nohup ./script.sh < inputFile.txt > ./logFile 2>&1 &
inputFile.txt can be any file. If your file has no input then we usually use /dev/null. So the command would be:
nohup ./script.sh < /dev/null > ./logFile 2>&1 &
After that close your bash session,open another terminal and execute: ps -aux | egrep "script.sh" and you will see that your script is still running at the background. Of cource,if you want to stop it then execute the same command (ps) and kill -9 <PID-OF-YOUR-SCRIPT>
See Bash Service Manager project: https://github.com/reduardo7/bash-service-manager
Implementation example
#!/usr/bin/env bash
export PID_FILE_PATH="/tmp/my-service.pid"
export LOG_FILE_PATH="/tmp/my-service.log"
export LOG_ERROR_FILE_PATH="/tmp/my-service.error.log"
. ./services.sh
run-script() {
local action="$1" # Action
while true; do
echo "### Running action '${action}'"
echo foo
echo bar >&2
[ "$action" = "run" ] && return 0
sleep 5
[ "$action" = "debug" ] && exit 25
done
}
before-start() {
local action="$1" # Action
echo "* Starting with $action"
}
after-finish() {
local action="$1" # Action
local serviceExitCode=$2 # Service exit code
echo "* Finish with $action. Exit code: $serviceExitCode"
}
action="$1"
serviceName="Example Service"
serviceMenu "$action" "$serviceName" run-script "$workDir" before-start after-finish
Usage example
$ ./example-service
# Actions: [start|stop|restart|status|run|debug|tail(-[log|error])]
$ ./example-service start
# Starting Example Service service...
$ ./example-service status
# Serive Example Service is runnig with PID 5599
$ ./example-service stop
# Stopping Example Service...
$ ./example-service status
# Service Example Service is not running
Here is the minimal change to the original proposal to create a valid daemon in Bourne shell (or Bash):
#!/bin/sh
if [ "$1" != "__forked__" ]; then
setsid "$0" __forked__ "$#" &
exit
else
shift
fi
trap 'siguser1=true' SIGUSR1
trap 'echo "Clean up and exit"; kill $sleep_pid; exit' SIGTERM
exec > outfile
exec 2> errfile
exec 0< /dev/null
while true; do
(sleep 30000000 &>/dev/null) &
sleep_pid=$!
wait
kill $sleep_pid &>/dev/null
if [ -n "$siguser1" ]; then
siguser1=''
echo "Wait was interrupted by SIGUSR1, do things here."
fi
done
Explanation:
Line 2-7: A daemon must be forked so it doesn't have a parent. Using an artificial argument to prevent endless forking. "setsid" detaches from starting process and terminal.
Line 9: Our desired signal needs to be differentiated from other signals.
Line 10: Cleanup is required to get rid of dangling "sleep" processes.
Line 11-13: Redirect stdout, stderr and stdin of the script.
Line 16: sleep in the background
Line 18: wait waits for end of sleep, but gets interrupted by (some) signals.
Line 19: Kill sleep process, because that is still running when signal is caught.
Line 22: Do the work if SIGUSR1 has been caught.
Guess it does not get any simpler than that.
Like many answers this one is not a "real" daemonization but rather an alternative to nohup approach.
echo "script.sh" | at now
There are obviously differences from using nohup. For one there is no detaching from the parent in the first place. Also "script.sh" doesn't inherit parent's environment.
By no means this is a better alternative. It is simply a different (and somewhat lazy) way of launching processes in background.
P.S. I personally upvoted carlo's answer as it seems to be the most elegant and works both from terminal and inside scripts
try executing using &
if you save this file as program.sh
you can use
$. program.sh &