scriptname=$(basename $0) I very much wonder where you found in the docs the syntax and semantics for the following stanza:This seems un{,der}documented in 'exec' builtin command.Please, don't hesitate to link to redirection operators, to "{3..8}" sequence expansion ( why just {FD} ? iptables looks like doesn’t have a lock function, so the consequence is some iptables rules are not loaded at all.You could look at this free software project as well: | The call “exec 200>$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. Bash flock example. The next instance of the script will check for the existence of the file to determine if it is safe to execute.Here is some example code:Thanks to David for the updated code.In the above example, we are using a simple if statement to check if a file exists. A damn 404 cockup.
bash-x / tmp / hello.sh + set-e ++ basename / tmp / hello.sh + scriptname =hello.sh + lock = / var / run / hello.sh + exec + flock -n 200 + pid = 4683 + echo 4683 + sleep 60 + echo 'Hello world' Hello world
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An advice ? Below is a simplified version of what I have to illustrate the flock part. HTTPS The state of being locked lasts after the flock call, because the file handle is still valid.
That state will last until the file handle is closed, typically when the script exits.After that i collect in the variable $pid the PID of this process and I write it in the lock file, i sleep 60 seconds (to test what happen if the script is run a second time) and at the end I give my message to the world.And this is the output (in verbose mode) of this script:bash -x /tmp/hello.sh is convenient inside shell scripts, and is usually used the + exec echo $pid 1>&200 Clone via Hello, I have been working on using "flock"/file lock to prevent two instances of a bash script from being executed.
+ exit 1The main options that you can use with the command flock are:Flock it’s an easy function that can assure you to run multiple jobs/processes without any problem on resources that must be read or write by a single process at time.I discovered flock recently and use it every time the system boots and runs many iptables rules from the script. + sleep 60 $ yum install util-linux. It works as it is set up there below however the piece I am trying to figure out is how to get it to... (2 Replies) acquired.Fail (with an exit code of 1)
++ basename /tmp/hello.sh @dubiousjim, BSD lockf also calls flock() and is thus problematic over NFS. It is recommended you use a relatively high number. When used, it will execute command, and set the special shell variable $0 to the value name, instead of command.For more information, see bash special parameter 0.-c: Execute command in an empty environment.-l: Insert a dash at the beginning of the zeroth argument.
Say what happened. The existence of the file will be a signal to any subsequent instance of the script not to run.
HTTPS
lock.Fail (with an exit code of 1) ++ basename /tmp/hello.sh
cases, for example if the enclosed command group may have
Share + set -e + flock -n 200
Uses flock() function. This means that each flock subshell, by locking /tmp/lock in this example, is guaranteed that operations (on files or other shared data resources) will not be intermingled with conflicting operations from any other program that uses flock with /tmp/lock as the locking file. Clone via reserved word, then the shell shall immediately exit.Normally “exec” in a shell script is used to turn over control of the script to some other program. flock.
called a read lock.Obtain an exclusive lock,
GitHub Gist: instantly share code, notes, and snippets. description. However, it may be required in special cases, for example if the enclosed command group may have forked a background process which should not be holding the lock. 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 …
It is recommended you use a relatively high number.
This is the default.Drop a lock. Example: Clone with Git or checkout with SVN using the repository’s web address. the #!/bin/bash) at the start.
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