1、前言
時間對操作系統來說非常重要，從內核級到應用層，時間的表達方式及精度各部相同。linux內核里面用一個名為jiffes的常量來計算時間戳。應用層有time、getdaytime等函數。今天需要在應用程序獲取系統的啟動時間，百度了一下，通過sysinfo中的uptime可以計算出系統的啟動時間。
2、sysinfo結構
sysinfo結構保持了系統啟動后的信息，主要包括啟動到現在的時間，可用內存空間、共享內存空間、進程的數目等。man sysinfo得到結果如下所示：
1 struct sysinfo { 2 long uptime; /* Seconds since boot */ 3 unsigned long loads[3]; /* 1, 5, and 15 minute load averages */ 4 unsigned long totalram; /* Total usable main memory size */ 5 unsigned long freeram; /* Available memory size */ 6 unsigned long sharedram; /* Amount of shared memory */ 7 unsigned long bufferram; /* Memory used by buffers */ 8 unsigned long totalswap; /* Total swap space size */ 9 unsigned long freeswap; /* swap space still available */ 10 unsigned short procs; /* Number of current processes */ 11 char _f[22]; /* Pads structure to 64 bytes */ 12 };
3、獲取系統啟動時間
通過sysinfo獲取系統啟動到現在的秒數，用當前時間減去這個秒數即系統的啟動時間。程序如下所示：
1 #include <stdio.h> 2 #include <sys/sysinfo.h> 3 #include <time.h> 4 #include <errno.h> 5 6 static int print_system_boot_time() 7 { 8 struct sysinfo info; 9 time_t cur_time = 0; 10 time_t boot_time = 0; 11 struct tm *ptm = NULL; 12 if (sysinfo(&info)) { 13 fprintf(stderr, "Failed to get sysinfo, errno:%u, reason:%s\n", 14 errno, strerror(errno)); 15 return -1; 16 } 17 time(&cur_time); 18 if (cur_time > info.uptime) { 19 boot_time = cur_time - info.uptime; 20 } 21 else { 22 boot_time = info.uptime - cur_time; 23 } 24 ptm = gmtime(&boot_time); 25 printf("System boot time: %d-%-d-%d %d:%d:%d\n", ptm->tm_year + 1900, 26 ptm->tm_mon + 1, ptm->tm_mday, ptm->tm_hour, ptm->tm_min, ptm->tm_sec); 27 return 0; 28 } 29 30 int main() 31 { 32 if (print_system_boot_time() != 0) { 33 return -1; 34 } 35 return 0; 36 }
測試結果如下所：
