dotlockfile

dotlockfile [-v] [-r retries] [-t timeout] lockfile [command...]

lockfile
    The path to the lockfile to be created or tested.

-v
    Be verbose; print informational messages to standard error.

-r retries
    Specify the number of times to retry creating the lockfile if it already exists. If retries is 0, the command fails immediately if the lockfile exists.

-t timeout
    Specify the timeout (in seconds) for retrying the lockfile creation. If the lock is not acquired within the timeout period, the command fails.

[command...]
    An optional command to execute while the lockfile is held. The lockfile is released when the command completes.

The dotlockfile command provides a mechanism for creating and managing lockfiles in a safe and robust manner. It's designed to prevent race conditions and ensure exclusive access to resources or data. It works by creating a lockfile (typically in a directory specified by the user) and providing options to test for its existence, create it (atomically), and remove it. The key feature is its atomicity; the creation process is guaranteed to be atomic, preventing multiple processes from simultaneously claiming the lock. The utility supports several methods for handling lockfile creation and deletion, allowing users to adapt its behavior to their specific needs. Its core benefit resides in its ability to guarantee mutually exclusive access to shared resources, mitigating potential data corruption or inconsistent state issues, especially in concurrent environments. Properly used, it drastically improves the reliability of shell scripts and programs that require synchronization mechanisms.

The `dotlockfile` command relies on the underlying filesystem's atomicity guarantees. Some network filesystems may not provide the necessary guarantees, which can lead to race conditions if the lockfile is created in a shared network location.
Ensure the target directory for the lockfile exists and is accessible with the necessary permissions.
The command does not automatically handle orphaned lockfiles (left behind by a process that crashed). Consider implementing a mechanism to detect and remove such lockfiles based on timestamp or process ID checking.

The dotlockfile command returns 0 on success (lock acquired or already held, and command, if given, executed successfully), and a non-zero value on failure (e.g., lock acquisition failed, command execution failed).

The command attempts to handle signals gracefully. If a signal is received while waiting for the lock, it will typically exit with an appropriate error code. The command will release the lock before exiting, if it holds one.

The `dotlockfile` utility has been available for a long time as part of various scripting toolsets. It's evolved to provide a relatively simple and reliable mechanism for managing lockfiles. Its original development was motivated by the need for reliable synchronization in shell scripts, especially in scenarios where multiple scripts or processes might attempt to access the same resources simultaneously. It is a part of Mailutils (gnu.org/software/mailutils) tool suite now.

flock(1), lockfile-create(1), lockfile-remove(1)