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Questions tagged [flock]

26 questions
19
votes
1 answer

Why flock doesn't clean the lock file?

After process is completed, I see that the lock file isn't deleted? Is there any reason that why flock keeps the file ? Also how does flock knows if there is a lock acquired ? Here is the example from a crontab file * * * * * flock python…
wayfare
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14
votes
4 answers

Pass multiple commands to flock

flock -x -w 5 ~/counter.txt 'COUNTER=$(cat ~/counter.txt); echo $((COUNTER + 1)) > ~/counter.txt' How would I pass multiple commands to flock as in the example above? As far as I understand, flock takes different flags (-x for exclusive, -w for…
d-_-b
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8
votes
3 answers

Handling of stale file locks in Linux and robust usage of flock

I have a script I execute via cron regularly (every few minutes). However the script should not run multiple times in parallel and it sometimes runs a bit longer, thus I wanted to implement some locking, i.e. making sure the script is terminated…
hanno
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8
votes
1 answer

Flock doesn't seem to be working

I've recently been trying to create a shell script for a minor project, and for some reason, the flock command isn't working for me properly. Whenever I invoke it in a subshell the atomic way and put it into the background, other programs seem to…
Mr. Minty Fresh
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6
votes
1 answer

How to do locking a file from a shell script?

I would like to synchronize two Bash scripts via a file lock. How to do this? Zsh has zsystem flock call, but is there a more "shellish" method that's also available to Bash?
Itzie
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5
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3 answers

Flocking a filedescriptor in a shell script

I thought this would give me uninterrupted begin-end pairs, but it doesn't: #!/bin/bash fun()( flock 1 || { echo >&2 "$BASHPID: FAIL: $?"; exit 1; } echo "$BASHPID begin" sleep 1; echo "$BASHPID end" ) fun & fun & fun & fun & fun…
Petr Skocik
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3
votes
1 answer

Check and Test Lock from other Process

I am trying to create a service wrapper (init.d script) around one of my favorite applications. The application creates both a PID and a lock file, and so I'm trying to use those to ensure that I can report accurate status of the application and…
palswim
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2
votes
1 answer

Cannot get bash flock to work

I derived a sample bash script from what I have seen around, regarding bash flock function. I do: func() { 42>/home/foo flock -e 42 || exit 1 echo "hello world" sleep 5 } Then I consecutively run func&, each of which prints hello…
corsel
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1
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0 answers

Ubuntu user not affected by sticky bit on Ubuntu 22.04

I experience a strange behaviour in stick bit on /tmp directory and flock command. Tried with two cases: Case 1: create file with Ubuntu user, root have no access to the created file. ubuntu@:~$ touch -a /tmp/ubuntu_user_created.lck ubuntu@:~$ flock…
Tien Dung Tran
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1
vote
0 answers

Is this flock usage with if-else safe?

I have two shell scripts that may be run in parallel but may also be run one at a time. Both scripts rely on an initial setup step that takes a while and can't be run by both at the same time. To allow for parallel execution for the remainder, I've…
Etheryte
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1
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2 answers

Using flock fails with zsh but works in bash?

Employing the mechanism from the answer at https://unix.stackexchange.com/a/274499/5132 in the Z shell: ( flock -x 200 echo "test"; ) 200>mylockfile2 returns zsh: parse error near `200' While in bash it works correctly. What may be the issue…
Chris Stryczynski
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0
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0 answers

Force running a script using flock?

If given a lock on a script using flock(), is it possible to make a force run/unlock based on some argument passed to the script?
derwian36
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0
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2 answers

Shared locking of scripts that may call each other

This is unusual problem and probably it is the consequence of bad design. If somebody can suggest anything better, I'd happy to hear. But right now I want to solve it "as is". There is a bunch of interacting scripts. It doesn't matter for the sake…
Nikita Kipriyanov
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0
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1 answer

Testing file locking

I have a script which locks a file to avoid concurrent access to it, How can I execute this same script from two different terminals synchronously, to check if it works? Here is the script #!/bin/bash ( flock -xn 200 trap 'rm…
Rob
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0
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1 answer

Synchronizing access to shared, remote resource

I have a shared cache on a remote server that multiple clients are reading and writing to, so I need to synchronize access to this cache. I imagine I could: SSH into the remote and acquire a flock on the server Push the update to the server…
mola
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