Shell Script

Now a shell script can be written which uses the flock command to manage the locks on different files.

Script:

#!/bin/bash

echo "=============FILE LOCKING=============="
echo "Enter locking Mode (R/W): "
read mode
if [ "$mode" = "R" ]; then
    mode="-s"
else
    mode="-x"
fi

echo "Enter file path: "
read path

echo "Command to execute after locking: "
read command

runcommand="flock $mode $path -c '$command'"
eval "$runcommand"

Output:

Explanation:

1. The above shell script accepts the mode of locking from the user in the variable $mode.
2. For read, the ‘-s‘ argument is added to the command, and for write mode ‘-x‘ argument is added.
3. The file path to be locked is accepted as a string in the variable $path.
4. During the locking period, the command that has to be executed is then inputted in the variable $command.
5. The whole command to lock the file and execute the user’s command is created from the above parameters in variable $runcommand.
6. $runcommand is executed in the terminal.

Conclusion:

The above shell script can be used for flexible file locking according to the user’s needs. File locking can help during operations where mutual exclusion is required. Any file can be locked by providing the path to the file, locking mode, and the command to execute during the file locking, the script automatically generates the required command and performs the operation.

File-locking mechanisms can be implemented in Linux using shell scripts. Locking files is required and becomes necessary to make a mutual exclusion environment where multiple processes can read and write the same file without violating consistency issues. A typical race condition occurs when the output of particular commands is different based on the relative order of execution of commands. This can be solved by locking files when required.

Linux provides two types of locking mechanisms:

1. Shared Locks:

Also called a read lock. This lock can be applied to files being read by a process. This prevents other processes from acquiring a write lock on the same file thus the data can’t be modified as long as the process is reading it. Although a shared lock by some other process can still be acquired on the same file.

2. Exclusive Locks:

Also called the write lock. This lock can be used on a file being modified ie being written by any process. Acquiring this lock prevents other processes from getting both the shared and exclusive locks. Other processes must wait before getting a shared or exclusive lock till this process releases the lock.