14.1.1 指定需要的程式庫：ldd

使用指令 ldd 來釐清哪些程式庫將根據指定引數載入動態可執行檔。

tester@linux:~> ldd /bin/ls
        linux-gate.so.1 =>  (0xffffe000)
        librt.so.1 => /lib/librt.so.1 (0xb7f97000)
        libacl.so.1 => /lib/libacl.so.1 (0xb7f91000)
        libc.so.6 => /lib/libc.so.6 (0xb7e79000)
        libpthread.so.0 => /lib/libpthread.so.0 (0xb7e67000)
        /lib/ld-linux.so.2 (0xb7fb6000)
        libattr.so.1 => /lib/libattr.so.1 (0xb7e63000)
   

靜態二進位檔不需任何動態程式庫。

tester@linux:~> ldd /bin/sash
        not a dynamic executable
tester@linux:~> file /bin/sash
/bin/sash: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), for GNU/Linux 2.6.4, statically linked, for GNU/Linux 2.6.4, stripped
   

14.1.2 一個程式執行階段的程式庫呼叫：ltrace

指令 ltrace 讓您可以追蹤處理程序的程式庫呼叫。這個指令的用法與 strace 相似。參數 -c 會輸出程式庫呼叫的數目和持續時間。

tester@linux:~> ltrace -c find ~
% time     seconds  usecs/call     calls      function
------ ----------- ----------- --------- --------------------
 34.37    6.758937         245     27554 __errno_location
 33.53    6.593562         788      8358 __fprintf_chk
 12.67    2.490392         144     17212 strlen
 11.97    2.353302         239      9845 readdir64
  2.37    0.466754          27     16716 __ctype_get_mb_cur_max
  1.17    0.230765          27      8358 memcpy
[...]
  0.00    0.000036          36         1 textdomain
------ ----------- ----------- --------- --------------------
100.00   19.662715                105717 total
   

14.1.3 執行程式的系統呼叫：strace

公用程式 strace 可用來追蹤執行中處理程序的所有系統呼叫。將 strace 新增至指令行的開頭，以正常方式來輸入指令：

tester@linux:~> strace ls
execve("/bin/ls", ["ls"], [/* 61 vars */]) = 0
uname({sys="Linux", node="linux", ...}) = 0
brk(0)                                  = 0x805c000
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or \
    directory)
open("/etc/ld.so.cache", O_RDONLY)      = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=89696, ...}) = 0
mmap2(NULL, 89696, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7ef2000
close(3)                                = 0
open("/lib/librt.so.1", O_RDONLY)       = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0000\36\0"..., 512) \
   = 512
fstat64(3, {st_mode=S_IFREG|0755, st_size=36659, ...}) = 0
[...]
stat64(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 0), ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) \
    = 0xb7ca7000
write(1, "bin  Desktop  Documents  music\tM"..., 55bin  Desktop  Documents \
   \  music       Music  public_html  tmp
) = 55
close(1)                                = 0
munmap(0xb7ca7000, 4096)                = 0
exit_group(0)                           = ?
   

例如，要追蹤所有試圖開啟某一特定檔案的動作，可使用下列指令：

tester@linux:~> strace -e open ls .bashrc
open("/etc/ld.so.cache", O_RDONLY)      = 3
open("/lib/librt.so.1", O_RDONLY)       = 3
open("/lib/libacl.so.1", O_RDONLY)      = 3
open("/lib/libc.so.6", O_RDONLY)        = 3
open("/lib/libpthread.so.0", O_RDONLY)  = 3
open("/lib/libattr.so.1", O_RDONLY)     = 3
[...]
   

如果要追蹤所有子程序，可使用參數 -f。這樣便可充分掌控 strace 的行為和輸出格式。如需更多資訊，請參閱 man strace。