使用strace命令解决linux服务器依赖库问题

使用strace命令解决linux服务器依赖库问题

简单说明：
strace的另外一个用处是解决和动态库相关的问题。当对一个可执行文件运行ldd时，它会告诉你程序使用的动态库和找到动态库的位置。可是若是你正在使用一个比较老 的glibc版本（2.2或更早），你可能会有一个有bug的ldd程序，它可能会报告在一个目录下发现一个动态库，可是真正运行程序时动态链接程序 （/lib/ld-linux.so.2）却可能到另一个目录去找动态链接库。这一般由于/etc/ld.so.conf和 /etc/ld.so.cache文件不一致，或者/etc/ld.so.cache被破坏。在glibc 2.3.2版本上这个错误不会出现，可能ld-linux的这个bug已经被解决了。

尽管这样，ldd并不能把全部程序依赖的动态库列出 来，系统调用dlopen能够在须要的时候自动调入须要的动态库，而这些库可能不会被ldd列出来。做为glibc的一部分的NSS（Name Server Switch）库就是一个典型的例子，NSS的一个做用就是告诉应用程序到哪里去寻找系统账号数据库。应用程序不会直接链接到NSS库，glibc则会通 过dlopen自动调入NSS库。若是这样的库偶然丢失，你不会被告知存在库依赖问题，但这样的程序就没法经过用户名解析获得用户ID了。
让咱们看一个例子：
whoami程序会给出你本身的用户名，这个程序在一些须要知道运行程序的真正用户的脚本程序里面很是有用，whoami的一个示例 输出以下：
[root@mgr04 opt]# whoami
root

whoami程序会给出你本身的用户名，这个程序在一些须要知道运行程序的真正用户的脚本程序里面很是有用，whoami的一个示例 输出以下：

特别提示：演示系统环境以下

[root@mgr04 opt]# cat /etc/redhat-release 
CentOS Linux release 7.2.1511 (Core)

在centos系统命令行运行 ldd /usr/bin/whoami只能查看到whoami才依赖了2个库文件，然而实际上whoami 命令依赖系统的库文件远不止这些。

[root@mgr04 opt]# ldd /usr/bin/whoami
    linux-vdso.so.1 =>  (0x00007ffd1c111000)
    libc.so.6 => /lib64/libc.so.6 (0x00007fe374d4d000)
    /lib64/ld-linux-x86-64.so.2 (0x00007fe375116000)

我们能够经过 strace -e trace=open whoami 命令来查看实际中whoami 所调用的库文件以下：

查看命令行执行whoami命令是都打开了系统哪些依赖库文件：
[root@mgr04 opt]# strace -e trace=open whoami
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/nsswitch.conf", O_RDONLY|O_CLOEXEC) = 3
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
open("/lib64/libnss_files.so.2", O_RDONLY|O_CLOEXEC) = 3
open("/etc/passwd", O_RDONLY|O_CLOEXEC) = 3
root
+++ exited with 0 +++

故障模拟演示：
假设由于某种缘由在升 级glibc的过程当中负责用户名和用户ID转换的库NSS丢失，咱们能够经过把nss库更名来模拟这个环境

[root@mgr04 opt]# mv /lib64/libnss_files.so.2 /lib64/libnss_files.so.2.bak
[root@mgr04 opt]# 
[root@mgr04 opt]# whoami
whoami: cannot find name for user ID 0
[root@mgr04 opt]#

这里你能够看到，运行whoami时出现了错误，此时在命令行执行ldd程序的输出不会提供有用的帮助：

[root@mgr04 opt]# ldd /usr/bin/whoami
    linux-vdso.so.1 =>  (0x00007ffd62bd4000)
    libc.so.6 => /lib64/libc.so.6 (0x00007fdcf861f000)
    /lib64/ld-linux-x86-64.so.2 (0x00007fdcf89e8000)
[root@mgr04 opt]#

你只会看到whoami依赖Libc.so.6和ld-linux-x86-64.so.2，它没有给出运行whoami所必须的其余库。这里时用strace跟踪 whoami时的输出：

[root@mgr04 opt]# strace -o whoami-strace.txt whoami
whoami: cannot find name for user ID 0
[root@mgr04 opt]# cat whoami-strace.txt 
.....................
.....................
socket(AF_LOCAL, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
connect(3, {sa_family=AF_LOCAL, sun_path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
close(3)                                = 0
socket(AF_LOCAL, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
connect(3, {sa_family=AF_LOCAL, sun_path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
close(3)                                = 0
open("/etc/nsswitch.conf", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=1717, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f306e2ae000
read(3, "#\n# /etc/nsswitch.conf\n#\n# An ex"..., 4096) = 1717
read(3, "", 4096)                       = 0
close(3)                                = 0
munmap(0x7f306e2ae000, 4096)            = 0
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=28446, ...}) = 0
mmap(NULL, 28446, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f306e2a8000
close(3)                                = 0
open("/lib64/libnss_files.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("/lib64/tls/x86_64/libnss_files.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/lib64/tls/x86_64", 0x7fff92c1f600) = -1 ENOENT (No such file or directory)
open("/lib64/tls/libnss_files.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/lib64/tls", {st_mode=S_IFDIR|0555, st_size=4096, ...}) = 0
open("/lib64/x86_64/libnss_files.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/lib64/x86_64", 0x7fff92c1f600)   = -1 ENOENT (No such file or directory)
open("/lib64/libnss_files.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/lib64", {st_mode=S_IFDIR|0555, st_size=32768, ...}) = 0
open("/usr/lib64/tls/x86_64/libnss_files.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib64/tls/x86_64", 0x7fff92c1f600) = -1 ENOENT (No such file or directory)
open("/usr/lib64/tls/libnss_files.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib64/tls", {st_mode=S_IFDIR|0555, st_size=4096, ...}) = 0
open("/usr/lib64/x86_64/libnss_files.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib64/x86_64", 0x7fff92c1f600) = -1 ENOENT (No such file or directory)
open("/usr/lib64/libnss_files.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib64", {st_mode=S_IFDIR|0555, st_size=32768, ...}) = 0
munmap(0x7f306e2a8000, 28446)           = 0
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=28446, ...}) = 0
mmap(NULL, 28446, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f306e2a8000
close(3)                                = 0
open("/lib64/tls/libnss_sss.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("/lib64/libnss_sss.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("/usr/lib64/tls/libnss_sss.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("/usr/lib64/libnss_sss.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
munmap(0x7f306e2a8000, 28446)           = 0
open("/usr/share/locale/locale.alias", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=2502, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f306e2ae000
read(3, "# Locale name alias data base.\n#"..., 4096) = 2502
read(3, "", 4096)                       = 0
close(3)                                = 0
munmap(0x7f306e2ae000, 4096)            = 0
open("/usr/share/locale/en_US.UTF-8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en_US.utf8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en_US/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en.UTF-8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en.utf8/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/share/locale/en/LC_MESSAGES/coreutils.mo", O_RDONLY) = -1 ENOENT (No such file or directory)
write(2, "whoami: cannot find name for use"..., 39) = 39
close(1)                                = 0
close(2)                                = 0
exit_group(1)                           = ?
+++ exited with 1 +++
[root@mgr04 opt]#

你能够发如今不一样目录下面查找libnss.so.2的尝试，可是都失败了。若是没有strace这样的工具，很难发现这个错误是因为缺乏动态库形成的。现 在只须要找到libnss.so.2并把它放回到正确的位置就能够了。　

若是你已经知道你要找什么，你可让strace只跟踪一些类型的系统调用。例如，你须要看看在configure脚本里面执行的程序，你须要监视的系统调 用就是execve。让strace只记录execve的调用用这个命令：

strace -f -o configure-strace.txt -e execve ./configure

原文地址：
https://www.linuxidc.com/Linux/2012-12/75671p3.htm