How to use the command pmap (with examples)

The command pmap is used to report the memory map of a process or processes. It provides information about the memory usage of a specific process or multiple processes. This command can be especially useful for monitoring memory usage and identifying any memory-related issues in a process.

Use case 1: Print memory map for a specific process id (PID)

Code:

pmap pid

Motivation: Sometimes we need to know the memory usage of a specific process to troubleshoot memory-related issues or optimize memory usage. By using the pmap command with a specific process ID (PID), we can obtain a detailed memory map of that particular process.

Explanation: The pid parameter represents a specific process ID for which we want to retrieve the memory map. By running the command pmap pid, we can obtain information about the memory usage, including the memory addresses, permissions, and size of each memory segment of the specified process.

Example output:

Address     Kbytes     RSS    Anon  Locked Mode   Mapped File
00567000       340     240       -       - r-x--  libc-2.32.so
00950000       108     108       -       - r----  libc-2.32.so
00a94000         8       8       -       - rw---  libc-2.32.so
...

Use case 2: Show the extended format

Code:

pmap --extended pid

Motivation: When we need more detailed information about the memory map of a process, such as the range, offset, and major/minor device numbers for each memory segment, we can use the extended format of pmap.

Explanation: The --extended option is used with the pmap command to enable an extended format for displaying the memory map. By running the command pmap --extended pid, we can obtain additional information such as the range, offset, and major/minor device numbers for each memory segment of the specified process.

Example output:

Address           Kbytes     RSS  Dirty Mode  Mapping
0000000000400000       220     128    124 r-x--  a.out
0000000000600000        36      36     36 r----  a.out
0000000000605000         4       4      4 rw---  a.out
...

Use case 3: Show the device format

Code:

pmap --device pid

Motivation: The device format of pmap provides information about the major and minor device numbers associated with each memory segment. This can be useful when analyzing memory usage patterns or identifying any issues related to specific devices.

Explanation: The --device option is used with the pmap command to display the memory map in the device format. By running the command pmap --device pid, we can obtain information about the major and minor device numbers associated with each memory segment of the specified process.

Example output:

Address           Kbytes     RSS      Dirty Mode   Mapping
0000000000400000         -       -          - r-x--  a.out
0000000000600000         -       -          - r----  a.out
0000000000605000         -       -          - rw---  a.out
...

Use case 4: Limit results to a memory address range

Code:

pmap --range low,high

Motivation: Sometimes we are only interested in analyzing memory segments within a specific address range. In such cases, the --range option of pmap allows us to limit the output to the desired memory address range.

Explanation: The --range option is used with the pmap command to specify a memory address range in the format low,high. By running the command pmap --range low,high, where low and high represent the lower and upper bounds of the desired memory address range, we can obtain the memory map limited to that specific range.

Example output:

Address           Kbytes     RSS   Dirty Mode   Mapping
0000000000007000        24      12      12 r-x--  a.out
...

Use case 5: Print memory maps for multiple processes

Code:

pmap pid1 pid2 ...

Motivation: In situations where we need to monitor the memory usage of multiple processes simultaneously, the pmap command allows us to provide multiple process IDs as arguments. This way, we can obtain the memory maps for all the specified processes in a single command.

Explanation: By providing multiple process IDs (PID) as arguments to the pmap command, separated by spaces, we can retrieve the memory map for each of the specified processes. For example, running the command pmap pid1 pid2 ... will display the memory maps for all the processes with the given process IDs.

Example output:

Memory map for process 1001:
Address           Kbytes     RSS     Dirty  Mode   Mapping
0000000000400000       304     256       124  -r-x--  a.out
0000000000600000        36      36        36  -r----  a.out
0000000000605000         4       4         4  -rw---  a.out
...
Memory map for process 2001:
Address           Kbytes     RSS     Dirty  Mode   Mapping
0000000000400000       288     244       122  -r-x--  a.out
0000000000600000        36      36        36  -r----  a.out
0000000000605000         4       4         4  -rw---  a.out
...

Conclusion:

The pmap command is a versatile tool for analyzing and monitoring the memory usage of processes. With its various options and arguments, we can obtain detailed information about the memory map of a specific process or multiple processes. This can help us identify memory-related issues, optimize memory usage, and gain insights into the memory consumption patterns of a system.