lslocks

List all local system locks

$ lslocks

$ lslocks [[-o|--output]] [PID],[COMMAND],[PATH]

$ lslocks [[-r|--raw]] [[-n|--noheadings]]

$ lslocks [[-p|--pid]] [PID]

$ lslocks [[-J|--json]]

lslocks [options]

-b, --bytes
    Display the SIZE column in bytes rather than a human-readable format.

-i, --no-human-readable
    A synonym for --bytes.

-J, --json
    Use JSON output format.

-l, --list
    Use the list output format, where each lock is presented on a separate line.

-n, --noheadings
    Do not print a header line in the output.

-o, --output
    Specify which output columns to print. Use --help to see a list of all supported columns.

-p, --pid
    Display locks held by specific PIDs (comma-separated list of PIDs).

-r, --raw
    Use the raw output format, which might be easier for script parsing.

-S, --no-pager
    Do not use a pager for the output.

-s, --sort
    Sort output by the specified column name.

-t, --truncate
    Truncate output when columns are too wide, rather than wrapping.

-u, --no-empty-owner
    Do not print locks with an empty owner (e.g., locks from kernel threads).

-V, --version
    Display version information and exit.

-h, --help
    Display a help message and exit.

lslocks is a command-line utility used to display information about all currently held file locks on the local system. It provides details such as the command holding the lock, the process ID (PID), the lock type, mode (read/write), the number of lock owners, the device and path of the locked file, and the owner of the lock.

This command is particularly useful for diagnosing issues related to file access, such as "Text file busy" errors or unresponsive applications due to resource contention. It primarily focuses on advisory and mandatory locks on local filesystems and usually requires root privileges to view locks not owned by the current user.

Requires root privileges when listing locks not owned by the current user.
Does not show locks held by network file systems (e.g., NFS).

The TYPE column in lslocks output indicates the locking mechanism used. Common types include FLOCK (advisory locks managed by the flock(2) system call) and POSIX (locks managed by fcntl(2), which can be advisory or mandatory).

The MODE column describes the lock's access type. READ indicates a shared lock, allowing multiple processes to hold a read lock simultaneously. WRITE indicates an exclusive lock, preventing any other process from acquiring any type of lock (read or write) on the same region.

The BLOCKER column displays the PID of the process that is blocking the current lock request, if applicable. Conversely, the BLOCKED column (if enabled via -o) would show the PID of the process being blocked by the current lock.

Part of the util-linux project, lslocks was introduced to provide a dedicated and structured tool for listing file locks. Prior to its existence, this information was often harder to obtain, requiring more generic tools like lsof or fuser combined with manual interpretation. Its development aimed to offer a more direct and detailed insight into the file locking status on a Linux system.

fuser(1), lsof(8), flock(2), lockf(3)