Please contact the loosy team who maintains and develops this wonderful site by clicking in the mighty feedback button on the side of the page. echo "Hello world"Some explanation of the interesting parts of the code:When this option is on, if a simple command fails for any of the reasons listed in Consequences of Shell Errors or returns an exit status value >0, and is not part of the compound list following a while, until, or if keyword, and is not a part of an AND or OR list, and is not a pipeline preceded by the ! ++ basename /tmp/hello.sh

It is recommended you use a relatively high number. The state of being locked lasts after the flock call, because the file handle is still valid.

second forms wraps the lock around the executing a command, One thing to note, make sure you specify the shell to be used (i.e. ## The code: flock -n 200 || exit 1 An advice ? The noclobber option will work in ksh and bash. Peter Anvin .Can't remember a command ? This is the default.Drop a lock. Don't use set noclobber because you shouldn't be scripting in csh/tcsh. + scriptname=hello.sh The first and second forms wraps the lock around the executing a command, in a manner similar to su(1) or newgrp(1). file is closed. ... -c, --command Befehl übergibt einen einzelnen Befehl ohne Argumente an die Shell mit -c. -E, --conflict-exit-code Zahl ist der Exit-Code, wenn die Option -n verwendet wird und die kollidierende Sperrung besteht, oder wenn die Option -w verwendet und die Zeit überschritten wird. Recently a colleague of mine should run multiple parallel jobs on a server (around 20 in our specific case), every job does “an elaboration” and this can take a time longer or shorter in respect of the others, once a job finishes its task it must read from a text file the first line that indicate the ID of a new job, it removes that ID from the top of the text file and starts to elaborate it.Problem: On a long run (a run of 50K+ jobs) it happens “frequently” that 2 jobs finish at the same time and so both take the same ID causing problems to the whole process, we tried to use a simple lock file “touched” just after the job was opening the file with the list of ID, but it seems that this operation it’s too slow and we had some case of failed concurrency again.Perhaps a small example will help, this is my /tmp/hello.sh script:#!/bin/bash After my post Easy bash script locking with mkdir I got a lot of feedback and I've learned a lot about locking (Credits to my co-worker @nine_ch).. One thing I've learned: Linux has flock. Written by H. flock $0 cat $0 > lockfile__$0 # Set a lock on the script the above line appears in, #+ while listing the script to stdout. + echo 'Hello world'

Here's another way to do locking in shell script that can prevent the race condition you describe above, where two jobs may both pass line 3. Tells flock to exclusively lock the file referenced by file handle 200 or exit with code 1. Say what happened. The Overflow Blog Podcast 248: You can’t pay taxes if the website won’t load. not required, since a lock is automatically dropped when the The first and second forms wraps the lock around the executing a command, in a manner similar to su(1) or newgrp(1).It locks a specified file or directory, which is created (assuming appropriate permissions), if it does not already exist. Das Dienstprogramm flock(2) verwaltet Sperrungen über Shell-Skripte oder die Befehlszeile. flock:- Much less useful than the lockfile command is flock. The first and

The flock command is part of the util-linux package and is iptables looks like doesn’t have a lock function, so the consequence is some iptables rules are not loaded at all.You could look at this free software project as well: | The call “exec 200>$lock” will open the file named in $lock for reading, and assign it file handle 200I think “reading” should be “writing”, as referenced here This website uses cookies to improve your experience. if the lock cannot be acquired within Close the file descriptor on the #!/bin/bash) at the start. lock="/var/run/${scriptname}" But it can also be used to open a file and name a file handle for it.

I want to avoid any possibility of these various scripts running at the same time. Hello worldbash -x /tmp/hello.sh This is to prevent any other process from setting a lock on that file until completion of the specified command.

This site is made for you !A problem ? Nobody has to lose in work/life balance. scriptname=$(basename $0) That state will last until the file handle is closed, typically when the script exits. There is a tiny cockup. + exec called a read lock.Obtain an exclusive lock, An idea for a new feature ?

lock.Fail (with an exit code of 1) A command is missing ?Oops ! This is usually

pid=$$ cases, for example if the enclosed command group may have This utility manages flock(2) locks from within shell scripts or the command line.. + lock=/var/run/hello.sh exec 200>$lock

Just make sure your flock command references the number of the file descriptor applied. Thanks! + lock=/var/run/hello.sh The call “exec 200>$lock” will open the file named in $lock for reading, and assign it file handle 200Tells flock to exclusively lock the file referenced by file handle 200 or exit with code 1.

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