Getting started with embedded linux 3-7proc file system

overview

proc - process information pseudo-filesystem (process information virtual file system)

The proc file system is a virtual file system used to provide an interface to kernel data structures. Usually it is mounted in the /proc directory. Generally, the system will automatically mount this file system. Of course, you can also use the following command to mount it manually:

mount -t proc proc /proc # 可以看到proc文件系统的类型也为proc

Most of the files in this file system are read-only, but there are some writable files, and modifying these files can modify some kernel runtime variables.

From the name, this file system was only used to provide process-related information at the beginning, and later it was used to store other system-related information as it developed.

Files and Subdirectories

The files and subdirectories under the /proc directory are roughly divided into the following categories:

1. /proc/[pid] subdirectory
   This type of subdirectory is named after the pid of the corresponding process, and the files and subdirectories under it contain the running information of the corresponding process. For a process that uses multi-threading, there will generally be a task subdirectory under it, and the files in the subdirectory named after tid in the task subdirectory contain relevant information of each thread. These subdirectories are visible when traversing the /proc directory using the getdents() function, and can also be viewed using the ls command.

2. /proc/[tid] subdirectory
   is the same as the subdirectory named by each tid under /proc/[pid]/task/, but for the getdents() function and ls command, these directories are not visible.

3. /proc/self soft link
   A magical link, when a process accesses this directory, it is equivalent to accessing the /proc/[pid] directory corresponding to its own pid

4. The /proc/thread-self soft link
   is also a magical link. When a thread accesses this directory, it is equivalent to accessing the /proc/self/task/[tid] directory corresponding to its tid

5. /proc/[az]* Other files and subdirectories
   Commonly used files are as follows:

   file name	use
   cmdline	Record kernel boot parameters
   cmdline	Record kernel boot parameters
   cpuinfo	CPU related information
   iomem	Memory usage of IO devices
   interrupts	Display occupied interrupt and occupant information
   ioports	IO port usage
   girl	System physical memory image, unreadable
   loadavg	System load average
   meminfo	Physical memory and swap partition usage
   modules	List of loaded modules
   mounts	Information about mounted filesystems
   partitions	Partition table recognized by the system
   swaps	Swap partition utilization
   version	Kernel version information
   uptime	system uptime

Instructions

The program can directly use the standard IO or the file read and write functions of the C library to access the information in it, and use cat in the shell to directly print the file content.

A picture to get /proc

A picture clearly shows the ins and outs of the /proc directory:

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