This always works if I just type:if [ ! "$(pgrep vlc)" ]; then echo not running; else echo running; fi in the command prompt, but as soon as I make it a script, give it chmod +x and run it I always get "running" as the output. Can someone give me a lead?
#!/bin/bash
export DISPLAY=:0
if [ ! "$(pgrep vlc)" ]; then echo not running; else echo running; fi
If the name of your script contains 'vlc', pgrep founds that script running and condition in if is false, even though real VLC is not running.
You could insert
echo "$(pgrep vlc)"
before the if stament
You can be more selective with your pgrep command. It's not necessary to use command substitution and brackets.
#!/bin/bash
export DISPLAY=:0
if ! pgrep -f "/path/to/vlc " >/dev/null; then echo not running; else echo running; fi
another option to avoid mixup with your own script is to use ps's '-C' flag
(I dont know how portable it is though)
if ps -C vlc > /dev/null ; then echo running; else echo not runing; fi
Related
My script is executed by Cron and every 2 min checks if xxx is running. If it is not in the process then the script will run it. The problem is that sometimes it runs it several times.
My problem is how to detect that the program is running several times?
How does bash detect that the pidof function returns several rather than one pid?
#!/bin/bash
PID=`pidof xxx`
if [ "$PID" = "" ];
then
cd
cd /home/pi
sudo ./xxx
echo "OK"
else
echo "program is running"
fi
You can use this script for doing the same. It will make sure script is executed once.
#!/bin/bash
ID=`ps -ef|grep scriptname|grep -v grep|wc -l`
if [ $ID -eq 0 ];
then
#run the script
else
echo "script is running"
fi
I want to build a small script (called check_process.sh) that checks if a certain process $PROC_NAME is running. If it does, it returns its PID or -1 otherwise.
My idea is to use pgrep -f <STRING> in a command substitution.
If I run this code directly in the command line:
export ARG1=foo_name
export RES=$(pgrep -f ${ARG1})
if [[ $RES == "" ]]; then echo "-1" ; else echo "$RES"; fi
everything goes fine: PID or -1 depending on the process status.
My script check_process.sh contains the same lines plus an extra variable to pass the process' name :
#!/bin/bash
export ARG1=$1
export RES=$(pgrep -f ${ARG1})
if [[ $RES == "" ]]; then echo "-1" ; else echo "$RES"; fi
But this code does not work!
If the process is currently running I get two PIDs (the process' PID and something else...), whereas when I check a process that is not running I get the something else !
I am puzzled. Any idea?
Thanks in advance!
If you add the -a flag to pgrep inside your script, you can see something like that (I ran ./check_process.sh vlc):
17295 /usr/bin/vlc --started-from-file ~/test.mkv
18252 /bin/bash ./check_process.sh vlc
So the "something else" is the pid of the running script itself.
The pgrep manual explains the -f flag:
The pattern is normally only matched against the process name. When -f is set, the full command line is used.
Obviously, the script command line contain the lookup process name ('vlc') as an argument, hence it appears at the pgrep -f result.
If you're looking just for the process name matches you can remove the -f flag and get your desired result.
If you wish to stay with the -f flag, you can filter out the current pid:
#!/bin/bash
ARG1=$1
TMP=$(pgrep -f ${ARG1})
RES=$(echo "${TMP}" | grep -v $$)
if [[ $RES == "" ]]; then echo "-1" ; else echo "${RES}"; fi
Good day. I have a series of commands that I wanted to execute via a function so that I could get the exit code and perform console output accordingly. With that being said, I have two issues here:
1) I can't seem to direct stderr to /dev/null.
2) The first echo line is not displayed until the $1 is executed. It's not really noticeable until I run commands that take a while to process, such as searching the hard drive for a file. Additionally, it's obvious that this is the case, because the output looks like:
sh-3.2# ./runScript.sh
sh-3.2# com.apple.auditd: Already loaded
sh-3.2# Attempting... Enable Security Auditing ...Success
In other words, the stderr was displayed before "Attempting... $2"
Here is the function I am trying to use:
#!/bin/bash
function saveChange {
echo -ne "Attempting... $2"
exec $1
if [ "$?" -ne 0 ]; then
echo -ne " ...Failure\n\r"
else
echo -ne " ...Success\n\r"
fi
}
saveChange "$(launchctl load -w /System/Library/LaunchDaemons/com.apple.auditd.plist)" "Enable Security Auditing"
Any help or advice is appreciated.
this is how you redirect stderr to /dev/null
command 2> /dev/null
e.g.
ls -l 2> /dev/null
Your second part (i.e. ordering of echo) -- It may be because of this you have while invoking the script. $(launchctl load -w /System/Library/LaunchDaemons/com.apple.auditd.plist)
The first echo line is displayed later because it is being execute second. $(...) will execute the code. Try the following:
#!/bin/bash
function saveChange {
echo -ne "Attempting... $2"
err=$($1 2>&1)
if [ -z "$err" ]; then
echo -ne " ...Success\n\r"
else
echo -ne " ...Failured\n\r"
exit 1
fi
}
saveChange "launchctl load -w /System/Library/LaunchDaemons/com.apple.auditd.plist" "Enable Security Auditing"
EDIT: Noticed that launchctl does not actually set $? on failure so capturing the STDERR to detect the error instead.
I've written a script for me to start and stop my Perforce server. To shutdown the server I use the kill -SIGTERM command with the PID of the server daemon. It works as it should but there are some discrepancies in my script concerning the output behavior.
The script looks as follows:
#!/bin/sh -e
export P4JOURNAL=/var/log/perforce/journal
export P4LOG=/var/log/perforce/p4err
export P4ROOT=/var/local/perforce_depot
export P4PORT=1666
PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin"
. /lib/lsb/init-functions
p4start="p4d -d"
p4stop="p4 admin stop"
p4user=perforce
case "$1" in
start)
log_action_begin_msg "Starting Perforce Server"
daemon -u $p4user -- $p4start;
echo "\n"
;;
stop)
echo "BLABLA"
echo "$(pidof /usr/local/bin/p4d)"
#daemon -u $p4user -- $p4stop;
p4dPid="$(pidof /usr/local/bin/p4d)"
echo $p4dPid
if [ -z "$(pidof /usr/local/bin/p4d)" ]; then
echo "ERROR: No Perforce Server running!"
else
echo "SUCCESS: Found Perforce Server running!\n\t"
echo "Shutting down Perforce Server..."
kill -15 $p4dPid;
fi
echo "\n"
;;
restart)
stop
start
;;
*)
echo "Usage: /etc/init.d/perforce (start|stop|restart)"
exit 1
;;
esac
exit 0
When p4d is running the stop block works as intended, but when there is no p4d running the script with stop only outputs BLABLA and an empty new line because of the echo "$(pidof /usr/local/bin/p4d)". The error message stating that no server is running is never printed. What am I doing wrong here?
PS: The part if [ -z "$(pidof /usr/local/bin/p4d)" ]; then has been changed from if [ -z "$p4dPid" ]; then for debug reasons.
EDIT: I narrowed down the problem. If I don't use the p4dPid variable and comment out the lines p4dPid="$(pidof /usr/local/bin/p4d)" and echo $p4dPid the if block is processed and the error messages is printed. Still I don't unterstand what is causing this behavior.
EDIT 2: Problem solved!
The -e in #!/bin/sh -e was causing the shell to exit the script after any statement returning a non-zero return value.
When your service is not running, the command
echo "$(pidof /usr/local/bin/p4d)"
is processed as
echo ""
because pidof did not return any string. So the command outputs an empty line.
If you do not want this empty line, then just remove this statement, after all you print an error message when the process is not running.
Problem solved!
The -e in #!/bin/sh -e was causing the shell to exit after any statement returning a non-zero return value.
I have a script that runs every 15 minutes but sometimes if the box is busy it hangs and the next process will start before the first one is finished creating a snowball effect. How can I add a couple lines to the bash script to check to see if something is running first before starting?
You can use pidof -x if you know the process name, or kill -0 if you know the PID.
Example:
if pidof -x vim > /dev/null
then
echo "Vim already running"
exit 1
fi
Why don't set a lock file ?
Something like
yourapp.lock
Just remove it when you process is finished, and check for it before to launch it.
It could be done using
if [ -f yourapp.lock ]; then
echo "The process is already launched, please wait..."
fi
In lieu of pidfiles, as long as your script has a uniquely identifiable name you can do something like this:
#!/bin/bash
COMMAND=$0
# exit if I am already running
RUNNING=`ps --no-headers -C${COMMAND} | wc -l`
if [ ${RUNNING} -gt 1 ]; then
echo "Previous ${COMMAND} is still running."
exit 1
fi
... rest of script ...
pgrep -f yourscript >/dev/null && exit
This is how I do it in one of my cron jobs
lockfile=~/myproc.lock
minutes=60
if [ -f "$lockfile" ]
then
filestr=`find $lockfile -mmin +$minutes -print`
if [ "$filestr" = "" ]; then
echo "Lockfile is not older than $minutes minutes! Another $0 running. Exiting ..."
exit 1
else
echo "Lockfile is older than $minutes minutes, ignoring it!"
rm $lockfile
fi
fi
echo "Creating lockfile $lockfile"
touch $lockfile
and delete the lock file at the end of the script
echo "Removing lock $lockfile ..."
rm $lockfile
For a method that does not suffer from parsing bugs and race conditions, check out:
BashFAQ/045 - How can I ensure that only one instance of a script is running at a time (mutual exclusion)?
I had recently the same question and found from above that kill -0 is best for my case:
echo "Starting process..."
run-process > $OUTPUT &
pid=$!
echo "Process started pid=$pid"
while true; do
kill -0 $pid 2> /dev/null || { echo "Process exit detected"; break; }
sleep 1
done
echo "Done."
To expand on what #bgy says, the safe atomic way to create a lock file if it doesn't exist yet, and fail if it doesn't, is to create a temp file, then hard link it to the standard lock file. This protects against another process creating the file in between you testing for it and you creating it.
Here is the lock file code from my hourly backup script:
echo $$ > /tmp/lock.$$
if ! ln /tmp/lock.$$ /tmp/lock ; then
echo "previous backup in process"
rm /tmp/lock.$$
exit
fi
Don't forget to delete both the lock file and the temp file when you're done, even if you exit early through an error.
Use this script:
FILE="/tmp/my_file"
if [ -f "$FILE" ]; then
echo "Still running"
exit
fi
trap EXIT "rm -f $FILE"
touch $FILE
...script here...
This script will create a file and remove it on exit.