How to use the command 'ipcs' (with examples)

The ‘ipcs’ command is used to display information about resources used in IPC (Inter-process Communication). IPC is a mechanism provided by the operating system that allows processes to communicate with each other and synchronize their actions. The ‘ipcs’ command provides detailed information about the various IPC facilities such as message queues, shared memory segments, and semaphore arrays.

Use case 1: Specific information about the Message Queue which has the ID 32768

Code:

ipcs -qi 32768

Motivation: Sometimes, it is necessary to obtain specific information about a message queue in order to troubleshoot issues or monitor its usage. By using the ‘-qi’ option followed by the specific message queue ID, the ‘ipcs’ command can provide detailed information about that particular message queue.

Explanation: The ‘-qi’ option is used to specifically request information about a message queue by providing its ID as an argument. This command will display information such as the message queue ID, the owner of the queue, the process ID of the last message sender, the process ID of the last message receiver, the number of messages currently in the queue, the maximum number of bytes allowed per message, and the time of the last message send or receive.

Example output:

------ Message Queues --------
key        msqid      owner      perms      used-bytes   messages    
0x00008000 32768      john       600        0            0

In this example output, we can see that the message queue with the ID 32768 is owned by the user ‘john’, has a permission set of 600 (read and write access for the owner only), and currently has no messages in it.

Use case 2: General information about all the IPC

Code:

ipcs -a

Motivation: By using the ‘-a’ option, the ‘ipcs’ command can display general information about all IPC facilities on the system. This can be useful for monitoring overall system resource utilization and identifying potential issues with IPC resources.

Explanation: The ‘-a’ option is used to display information about all IPC facilities on the system. This command will provide information about all message queues, shared memory segments, and semaphore arrays. It displays information such as the resource type, resource ID, owner of the resource, permissions, and usage statistics.

Example output:

------ Message Queues --------
key        msqid      owner      perms      used-bytes   messages    
0x00008000 32768      john       600        0            0    
0x00008001 32769      jane       600        4            2   

------ Shared Memory Segments --------
key        shmid      owner      perms      bytes       nattch    
0x00008000 65536      john       600        1048576     2    
0x00008001 65537      jane       600        524288      1

------ Semaphore Arrays --------
key        semid      owner      perms      nsems    
0x00008000 98304      john       600        1    
0x00008001 98305      jane       600        1    

In this example output, we can see the general information about all IPC facilities on the system. It displays the message queues, shared memory segments, and semaphore arrays along with their respective IDs, owners, permissions, and usage statistics.

Conclusion:

The ‘ipcs’ command is a powerful tool for obtaining information about IPC resources on a system. It can be used to troubleshoot issues, monitor resource utilization, and identify potential problems. By using the ‘-qi’ option, specific information about a particular message queue can be obtained, while the ‘-a’ option provides a comprehensive overview of all IPC facilities on the system.