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flock

file managementLinux/Unix

The flock command is one of the most frequently used commands in Linux/Unix-like operating systems. flock Manage file locks from shell scripts

See Examples View Syntax

Quick Reference

Command Name:

flock

Category:

file management

Platform:

Linux/Unix

Basic Usage:

flock [options] [arguments]

Common Use Cases

Syntax

flock [options] file|directory command [arguments]

Options

Option	Description
`-s, --shared`	Get a shared lock (allowing other shared locks but not exclusive locks)
`-x, --exclusive`	Get an exclusive lock (the default)
`-n, --nonblock`	Fail (with an exit code of 1) rather than wait if the lock cannot be immediately acquired
`-w, --wait seconds`	Wait for a limited amount of time instead of indefinitely or failing immediately
`-o, --close`	Close file descriptor before running command
`-E, --conflict-exit-code number`	Use the specified exit code when conflict occurs (default is 1)
`-u, --unlock`	Drop a lock (usually not needed as locks are dropped automatically when the process terminates)
`-c, --command command`	Run a single command string through the shell

Examples

How to Use These Examples

The examples below show common ways to use the flock command. Try them in your terminal to see the results. You can copy any example by clicking on the code block.

# Basic Examples Basic

flock /tmp/lockfile.lock command args

Run command with arguments while holding a lock on /tmp/lockfile.lock.

flock -n /tmp/lockfile.lock command args

Run command with arguments, failing immediately if lock cannot be acquired.

flock -x /tmp/lockfile.lock command args

Obtain an exclusive lock (the default) and run command. # Advanced Examples Advanced flock -s /tmp/lockfile.lock command args Obtain a shared lock and run command. flock -o /tmp/lockfile.lock command args Close the file descriptor before executing command. flock -w 10 /tmp/lockfile.lock command args Wait up to 10 seconds to acquire the lock before failing. flock -E 63 -n /tmp/lockfile.lock command args Use exit code 63 instead of the default 1 when lock cannot be acquired. flock -c "command args" /tmp/lockfile.lock Run command in a shell while holding the lock on /tmp/lockfile.lock.

Try It Yourself

Practice makes perfect! The best way to learn is by trying these examples on your own system with real files.

Understanding Syntax

Pay attention to the syntax coloring: commands, options, and file paths are highlighted differently.

Notes

The flock command provides a way to manage file locks directly from shell scripts, enabling processes to coordinate access to shared resources. Key features of flock: 1. Process Synchronization: flock enables coordination between different processes by providing file-based locking mechanisms to prevent concurrent access to shared resources. 2. Lock Types: flock supports both exclusive locks (preventing all other processes from obtaining any lock) and shared locks (allowing other processes to obtain shared locks but not exclusive locks). 3. Non-blocking Option: With the -n option, flock can fail immediately if a lock cannot be obtained, which is useful for tasks that shouldn't wait. 4. Timeout Control: The -w option allows setting a maximum wait time for obtaining a lock, after which the command will fail if the lock couldn't be acquired. 5. Shell Integration: flock can run a command either directly or through a shell (using the -c option), making it flexible for various scripting needs. 6. File Descriptor Management: By default, the lock file is kept open for the duration of the command, but with the -o option, it can be closed before executing the command. 7. Custom Exit Codes: The -E option allows specifying a custom exit code when a lock conflict occurs, which can be useful for script flow control. Common use cases for flock include ensuring that cron jobs don't overlap, synchronizing access to shared data files, preventing concurrent execution of scripts, and implementing simple inter-process communication.

Related Commands

These commands are frequently used alongside flock or serve similar purposes:

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Use Cases

Learn By Doing

The best way to learn Linux commands is by practicing. Try out these examples in your terminal to build muscle memory and understand how the flock command works in different scenarios.

See Examples Try Lab Exercises

$ flock

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