How to use the command `lslocks` (with examples)

The lslocks command is used to list local system locks on a Linux system. It provides detailed information about the locks, including the process ID (PID), command, and file path associated with each lock. This command can be useful for troubleshooting or understanding processes that are holding locks on specific files.

Use case 1: List all local system locks

Code:

lslocks

Motivation: This use case is helpful when you want to see all the local system locks currently in place.

Explanation: Running the lslocks command without any additional arguments will list all the local system locks. The output includes the PID, COMMAND, and PATH columns by default.

Example output:

   PID                     COMMAND             PATH
     1                     systemd       /dev/sda3
     1                     systemd       /dev/sdb1
   738                      chrome       /home/user/file.txt
   876                        sshd       /var/run/sshd.pid

Use case 2: List locks with defined column headers

Code:

lslocks --output PID,COMMAND,PATH

Motivation: By specifying the desired output columns, this use case allows you to customize the information displayed when listing the locks. It can be helpful when you only need specific details about the locks.

Explanation: The --output option followed by the desired column headers allows you to specify which columns should be included in the output. In this example, we are including the PID, COMMAND, and PATH columns.

Example output:

   PID                     COMMAND             PATH
     1                     systemd       /dev/sda3
     1                     systemd       /dev/sdb1
   738                      chrome       /home/user/file.txt
   876                        sshd       /var/run/sshd.pid

Use case 3: List locks producing raw output (no columns), and without column headers

Code:

lslocks --raw --noheadings

Motivation: This use case is useful when you need to process the lock information programmatically or when you prefer a more concise output without any additional formatting.

Explanation: The --raw option removes any formatting, such as column alignment, from the output. The --noheadings option excludes the column headers from the output, resulting in a raw and compact list of locks.

Example output:

1 systemd /dev/sda3
1 systemd /dev/sdb1
738 chrome /home/user/file.txt
876 sshd /var/run/sshd.pid

Use case 4: List locks by PID input

Code:

lslocks --pid PID

Motivation: When you want to view locks associated with a specific process, using the PID as input allows you to narrow down the output and focus on the locks related to that process.

Explanation: The --pid option followed by the desired process ID (PID) restricts the output to only the locks associated with the specified process.

Example output:

   PID                     COMMAND             PATH
   738                      chrome       /home/user/file.txt

Use case 5: List locks with JSON output to stdout

Code:

lslocks --json

Motivation: When you need the lock information in a machine-readable format, using JSON output can make it easier to parse and integrate with other tools or applications.

Explanation: The --json option outputs the lock information in JSON format. This allows you to obtain the locks’ details as structured data, making it convenient for further processing or automation.

Example output:

[
  {
    "pid": 1,
    "command": "systemd",
    "path": "/dev/sda3"
  },
  {
    "pid": 1,
    "command": "systemd",
    "path": "/dev/sdb1"
  },
  {
    "pid": 738,
    "command": "chrome",
    "path": "/home/user/file.txt"
  },
  {
    "pid": 876,
    "command": "sshd",
    "path": "/var/run/sshd.pid"
  }
]

Conclusion:

The lslocks command is a powerful tool for examining and understanding the locks on a Linux system. By utilizing different options and arguments, you can customize the output format, filter locks by PID, and obtain the lock information in a machine-readable JSON format. Whether you need a comprehensive overview or specific lock details, lslocks provides the necessary functionality for effectively managing system locks.