命令介绍
strace是Linux环境下的一款程序调试工具，用来输出一个应用程序所使用的系统调用。
strace底层使用内核的ptrace特性来实现其功能。
什么是系统调用？
系统调用是通向操作系统本身的接口，是面向底层硬件的。通过系统调用，可以使得用户态运行的进程与硬件设备(如CPU、磁盘、打印机等)进行交互，是操作系统留给应用程序的一个接口。
常用选项
-t 在每行输出的前面显示时间(精确到秒)
-tt 在每行输出的前面显示时间(精确到毫秒)
-T 显示每次系统调用所花费的时间
-v 对于某些相关调用，显示详细信息(把完整的环境变量，文件stat结构等打出来)
-f 跟踪目标进程，以及目标进程创建的所有子进程
-e 指定要跟踪的系统调用
-o 把strace的输出写到文件中
-s 当系统调用的某个参数是字符串时，最多输出指定长度的内容，默认是32个字节
-p 指定要跟踪的进程pid, 要同时跟踪多个pid, 重复多次-p选项即可。
-c 统计每种系统调用所执行的时间，调用次数，出错次数。
使用
1.追踪打开文件的系统调用
[root@localhost ~]# strace cat /etc/hosts
execve("/usr/bin/cat", ["cat", "/etc/hosts"], 0x7fff79f5beb8 /* 26 vars */) = 0
brk(NULL) = 0x81e000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3cee950000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=20640, ...}) = 0
mmap(NULL, 20640, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f3cee94a000
close(3) = 0
open("/lib64/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0`&\2\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=2156240, ...}) = 0
mmap(NULL, 3985920, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f3cee362000
mprotect(0x7f3cee525000, 2097152, PROT_NONE) = 0
mmap(0x7f3cee725000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1c3000) = 0x7f3cee725000
mmap(0x7f3cee72b000, 16896, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f3cee72b000
close(3) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3cee949000
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3cee947000
arch_prctl(ARCH_SET_FS, 0x7f3cee947740) = 0
mprotect(0x7f3cee725000, 16384, PROT_READ) = 0
mprotect(0x60b000, 4096, PROT_READ) = 0
mprotect(0x7f3cee951000, 4096, PROT_READ) = 0
munmap(0x7f3cee94a000, 20640) = 0
brk(NULL) = 0x81e000
brk(0x83f000) = 0x83f000
brk(NULL) = 0x83f000
open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=106176928, ...}) = 0
mmap(NULL, 106176928, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f3ce7e1f000
close(3) = 0
fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 0), ...}) = 0
open("/etc/hosts", O_RDONLY) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=158, ...}) = 0
fadvise64(3, 0, 0, POSIX_FADV_SEQUENTIAL) = 0
read(3, "127.0.0.1 localhost localhost."..., 65536) = 158
write(1, "127.0.0.1 localhost localhost."..., 158127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4
::1 localhost localhost.localdomain localhost6 localhost6.localdomain6
) = 158
read(3, "", 65536) = 0
close(3) = 0
close(1) = 0
close(2) = 0
exit_group(0) = ?
+++ exited with 0 +++
2.显示系统调用的时间
[root@localhost ~]# strace -tt -T cat /etc/hosts
11:25:50.561449 open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 3 <0.000023>
11:25:50.561522 fstat(3, {st_mode=S_IFREG|0644, st_size=106176928, ...}) = 0 <0.000013>
11:25:50.561585 mmap(NULL, 106176928, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f7ecb038000 <0.000018>
11:25:50.561649 close(3) = 0 <0.000013>
11:25:50.561830 fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 0), ...}) = 0 <0.000017>
11:25:50.561908 open("/etc/hosts", O_RDONLY) = 3 <0.000024>
11:25:50.561979 fstat(3, {st_mode=S_IFREG|0644, st_size=158, ...}) = 0 <0.000014>
11:25:50.562046 fadvise64(3, 0, 0, POSIX_FADV_SEQUENTIAL) = 0 <0.000014>
11:25:50.562118 read(3, "127.0.0.1 localhost localhost."..., 65536) = 158 <0.000019>
11:25:50.562183 write(1, "127.0.0.1 localhost localhost."..., 158127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4
::1 localhost localhost.localdomain localhost6 localhost6.localdomain6
) = 158 <0.000018>
11:25:50.562244 read(3, "", 65536) = 0 <0.000014>
11:25:50.562304 close(3) = 0 <0.000016>
11:25:50.562386 close(1) = 0 <0.000013>
11:25:50.562443 close(2) = 0 <0.000012>
# 时间戳 # 花费的时间
3.跟踪特定系统调用
-e trace=file 文件相关的调用(参数中有文件名)
-e trace=process 进程管理相关的调用，比如fork/exec/exit_group
-e trace=network 网络通信相关的调用，比如socket/sendto/connect
-e trace=signal 信号相关的调用，比如kill/sigaction
-e trace=desc 和文件描述符相关，比如write/read/select/epoll等
-e trace=ipc 进程通信相关的调用，比如shmget等
# 跟踪文件访问相关系统调用
[root@localhost ~]# strace -e file cat /etc/hosts
execve("/usr/bin/cat", ["cat", "/etc/hosts"], 0x7fff79c90c58 /* 26 vars */) = 0
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
open("/lib64/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 3
open("/etc/hosts", O_RDONLY) = 3
4.跟踪多线程(进程)应用的系统调用
下面是一个多线程demo代码。
#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
void* ThreadA(void* par)
{
while(1)
{
printf("hello world\n");
sleep(1);
}
}
int main()
{
pthread_t t1;
pthread_create(&t1, NULL, ThreadA, NULL);
pthread_join(t1, NULL);
return 0;
}
编译代码
# gcc demo.c -o demo -lpthread
开始跟踪
# strace -ff -o out ./demo
执行完成后得到两个文件(每个线程一个)
# ls out.*
out.7611 out.7612
主线程 out.7611
mprotect(0x7fa0e4b6e000, 16384, PROT_READ) = 0
mprotect(0x7fa0e4d8f000, 4096, PROT_READ) = 0
mprotect(0x600000, 4096, PROT_READ) = 0
mprotect(0x7fa0e4fb6000, 4096, PROT_READ) = 0
munmap(0x7fa0e4faf000, 20776) = 0
set_tid_address(0x7fa0e4faca10) = 7611
set_robust_list(0x7fa0e4faca20, 24) = 0
rt_sigaction(SIGRTMIN, {sa_handler=0x7fa0e4b7f860, sa_mask=[], sa_flags=SA_RESTORER|SA_SIGINFO, sa_restorer=0x7fa0e4b88630}, NULL, 8) = 0
rt_sigaction(SIGRT_1, {sa_handler=0x7fa0e4b7f8f0, sa_mask=[], sa_flags=SA_RESTORER|SA_RESTART|SA_SIGINFO, sa_restorer=0x7fa0e4b88630}, NULL, 8) = 0
rt_sigprocmask(SIG_UNBLOCK, [RTMIN RT_1], NULL, 8) = 0
getrlimit(RLIMIT_STACK, {rlim_cur=8192*1024, rlim_max=RLIM64_INFINITY}) = 0
mmap(NULL, 8392704, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_STACK, -1, 0) = 0x7fa0e3faa000
brk(NULL) = 0x15c8000
brk(0x15e9000) = 0x15e9000
brk(NULL) = 0x15e9000
mprotect(0x7fa0e3faa000, 4096, PROT_NONE) = 0
clone(child_stack=0x7fa0e47a9fb0, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID, parent_tidptr=0x7fa0e47aa9d0, tls=0x7fa0e47aa700, child_tidptr=0x7fa0e47aa9d0) = 7612
futex(0x7fa0e47aa9d0, FUTEX_WAIT, 7612, NULL) = 0
exit_group(0) = ?
+++ exited with 0 +++
工作线程 out.7612
set_robust_list(0x7fa0e47aa9e0, 24) = 0
fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 0), ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fa0e4fb4000
write(1, "hello world\n", 12) = 12
madvise(0x7fa0e3faa000, 8368128, MADV_DONTNEED) = 0
exit(0) = ?
+++ exited with 0 +++