Introduction to Proc File System

• The proc file system provides information on the current status of the Linux kernel and running process.
• It also allows modifications of kernel parameters in simple ways during runtime
• Each process in the system that is currently running is assigned a directory /proc/pid, where pid is the process identification number of the relevant process
• There are also files and directories for process independent information such as loaded modules, used bus systems etc.

Disadvantages of Proc

• There is no interface for the individual files, every user has to find out where and how the information that is required is hidden in the file
• Another disadvantage is that all information is output as strings, therefore conversion is always necessary for further processing

Structure of File system

struct proc_dir_entry

{

unsigned short low_ino; //inode number

unsigned short namelen; //length of the name

const char *name; //name of the entry

mode_t mode; //mode

uid_t uid; //User ID

gid_t gid; //Group ID

unsigned long size; //size of the file

struct inode_operations *proc_iops; //inode-op

struct file_operations *proc_fops; //file-op

struct proc_dir_entry *next, *parent, *subdir; //connection

….

}

The above structure is as PD entry.

• The pointer next, parent, subdir are used for linking. Next shows the next entry in the current directory, parent shows the parent directory (root directory), and subdir shows a subdirectory. This can be implemented like the following loop

for(de=de->subdir ; de; de=de->next){

…..

}

• the file and the directory entries are lying under the /proc/ directory