Linux Proc file system experiment (CODE)

The/proc directory on Linux is a file system called proc file system (Virtual File System). It stores kernel status information, including cpu, memory, and processes. The proc file system has many advantages: applications do not need to switch to the kernel state to obtain kernel data, which increases system security (for example, the ps command is to obtain process information through proc ); applications can directly change kernel parameters through proc, so that they can change and optimize kernel behavior without re-compiling the kernel. In short, proc provides a secure and convenient interface for your applications to obtain internal system information. Proc is in memory and does not occupy external memory.

The files in the/proc directory are as follows:

Apm	Advanced Power Management Information
Cmdline	Kernel command line
Cpuinfo	Cpu Information
Devices	Available devices (Block devices/character devices)
Dma	Used DMS channels
Filesystems	Supported file systems
Interrupts	Interrupted use
Ioports	I/O port usage
Kcore	Core kernel impressions
Kmsg	Kernel message
Ksyms	Kernel symbol table
Loadavg	Server Load balancer
Locks	Kernel lock
Meminfo	Memory Information
Misc	Miscellaneous
Modules	Load module list
Mounts	File System loaded
Partitions	Partition Table recognized by the System
Rtc	Real time clock
Slabinfo	Slab pool info
Stat	Comprehensive statistics Status table
Swaps	Utilization of swap space
Version	Kernel version
Uptime	Normal system running time

The following is a program that I wrote to view the cpu and kernel version information and startup time:

Because file read and write operations are involved, first introduce several File Read and Write Functions.

1) fgetc reads a character from the stream and adds the position of the file pointer. It is often used with EOF to read all the characters in the stream.

2) putchar outputs a character to the terminal.

3) fgets (char * s, int size, FILE * stream) reads a row from the FILE stream to s. The size is generally the size of the array s, s ends with the character '/0.

4) int feof (FILE * stream) determines whether a FILE ends. If yes, a non-zero value is returned; otherwise, the value is 0.

5) int fscanf (FILE * stream, const char * format,...) formatted input from the FILE stream (or standard input), usage:

#include<stdio.h>int main(){       int i;    char s[5];    fscanf(stdin, "%d %5[a-z]%*s", &i, s);    printf("%d %s \n", i, s);    return 0;    }

Execution result (enter 99 abcdefghijk in the command line. Because fscanf encounters a space and ends with a line change, 99 is saved to I and abcde is saved to s ):

#include<stdio.h>#include<sys/time.h>#define LB_SIZE 80enum TYPE{STANDARD, SHORT, LONG};FILE *thisProcFile; //Proc open file pointerstruct timeval now; //system time dateenum TYPE reportType; //the type of observation reportchar repTypeName[16];char *lineBuf; //read out bufferint interval; //system overload detect intervalint duration; //system overload detect durationint iteration;char c1, c2; //character handle uintvoid getTwoTime(FILE *fp) {long uptime, idletime;int day, hour,minute, second;int m, n;char temp[80];m = n = 0;int ret;int i = 0;char s[100][100];int j;while((ret=fscanf(fp, "%s", s[i])) != EOF) i++;//printfor(j = 0; j < i; j++){printf("%s\n", s[j]);}uptime = atol(s[0]);idletime = atol(s[1]);printf("<<---------------------___________------------------------->\n");printf("the uptime of system -----------------------------> %ld\n", uptime);printf("the idletime of process -----------------------------> %ld\n", idletime);printf("<<---------------------___________------------------------->\n");/*time_t uptime_timet = uptime;printf("xixixixixi%ld\n", uptime_timet);char *result = ctime(&uptime_timet); printf("hahahahahahah %s\n", result);*/int days;int hours;int minutes;int seconds;//uptime of systemdays = (int)uptime/86400;hours = (int)uptime%86400/3600;minutes = (int)uptime%3600/60;seconds = (int)uptime%3600%60;printf("the uptime of system-------------days %d----hours %d-----minutes %d-----seconds %d----\n", days, hours, minutes, seconds);//idletimedays = (int)idletime/86400;hours = (int)idletime%86400/3600;minutes = (int)idletime%3600/60;seconds = (int)idletime%3600%60;printf("the idletime of system-------------days %d----hours %d-----minutes %d-----seconds %d----\n", days, hours, minutes, seconds);}//get time from startingvoid sampleTime(){//open timer fileFILE *fp;if((fp=fopen("/proc/uptime", "r")) == NULL){printf("not open /proc/uptime");exit(0);}getTwoTime(fp);fclose(fp);}void getCPUinfo(){FILE *cpuinfo;char ch;if((cpuinfo=fopen("/proc/cpuinfo","r")) == NULL){printf("not open /proc/cpuinfo");exit(0);}/*while((ch=fgetc(cpuinfo)) != EOF)putchar(ch);fclose(cpuinfo);*/printf("*********************cpu*******************\n");while(!feof(cpuinfo)){fgets(lineBuf, LB_SIZE+1, cpuinfo);printf("%s", lineBuf);}fclose(cpuinfo);}void getKernelVersion() {FILE *version;char ch;if((version=fopen("/proc/version","r")) == NULL){printf("not open /proc/version");exit(0);}printf("*****************version*************************\n");while(!feof(version)){fgets(lineBuf, LB_SIZE+1, version);printf("%s", lineBuf);}fclose(version);}int main(int argc, char *argv[]) {lineBuf = (char *)malloc(LB_SIZE + 1);reportType = STANDARD;strcpy(repTypeName, "Standard");if(argc > 1) {sscanf(argv[1], "%c%c", &c1, &c2);if(c1 != '-')  exit(1);if(c2 == 'b'){printf("********************************Memory Info*********************************\n");//open memory info FILE *meminfo; char ch;if((meminfo=fopen("/proc/meminfo","r")) == NULL){printf("not open /proc/meminfo");exit(0);}while((ch=fgetc(meminfo)) != EOF)putchar(ch);fclose(meminfo);printf("********************************TIME*********************************\n");//cat the start timesampleTime();} else if(c2 == 'c'){//get cpu info and kernel versionprintf("*************************CPU & kernel*************************\n");getCPUinfo();getKernelVersion();}}}

Run:

./Main-B view the memory information and formatted start time.

./Main-c view CPU type and kernel version.