Linux command – ldconfig & ldd

測試環境為 CentOS 6 x86_64 虛擬機.

Linux 上大部分的程式是採用 Dynamical Link 方式來編譯,我們可以透過 ldconfig 或是 ldd 來觀察 dynamically linked (uses shared libs) 的狀態.

ldconfig – configure dynamic linker run-time bindings

哪一些函數庫需要再開機的時就預先載入到記憶體,這定義在 /etc/ld.so.conf 檔案裡面.

[root@localhost ~]# cat /etc/ld.so.conf 
include ld.so.conf.d/*.conf
/usr/local/lib

使用者通常可以自行定義在 /etc/ld.so.conf.d/*.conf ,像是 vmware 就定義了 vmware-tools-libraries.conf .

[root@localhost ~]# cat /etc/ld.so.conf.d/vmware-tools-libraries.conf 
/usr/lib/vmware-tools/lib32/libvmGuestLib.so
/usr/lib/vmware-tools/lib64/libvmGuestLib.so
/usr/lib/vmware-tools/lib32/libvmGuestLibJava.so
/usr/lib/vmware-tools/lib64/libvmGuestLibJava.so
/usr/lib/vmware-tools/lib32/libDeployPkg.so
/usr/lib/vmware-tools/lib64/libDeployPkg.so

透過 ldconfig 指令來看目前哪一些函數庫已經被載入

[root@localhost ~]# ldconfig -p | grep -i vmguest
	libvmGuestLibJava.so (libc6,x86-64) => /usr/lib/vmware-tools/lib64/libvmGuestLibJava.so/libvmGuestLibJava.so
	libvmGuestLibJava.so (libc6) => /usr/lib/vmware-tools/lib32/libvmGuestLibJava.so/libvmGuestLibJava.so
	libvmGuestLib.so (libc6,x86-64) => /usr/lib/vmware-tools/lib64/libvmGuestLib.so/libvmGuestLib.so
	libvmGuestLib.so (libc6) => /usr/lib/vmware-tools/lib32/libvmGuestLib.so/libvmGuestLib.so

ldconfig 參數:
-p : Print the lists of directories and candidate libraries stored in the current cache.

ldd – print shared library

ldd 是個 script file 如果想知道該程式使用了哪一些 Libary 就可以使用 ldd 來觀看.

首先哪些程式使用了動態連結 dynamically linked (使用共享函數庫 shared libs) ,可以先透過 file 指令來觀看.

[root@localhost ~]# file /bin/ls
/bin/ls: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.18, stripped

指令 ls 的確有使用 dynamically linked (uses shared libs) ,這時候可以透過 ldd 來檢視他使用了哪一些動態連結函數庫 (so 檔).

[root@localhost ~]# ldd /bin/ls
	linux-vdso.so.1 =>  (0x00007ffe62d78000)
	libselinux.so.1 => /lib64/libselinux.so.1 (0x0000003bf4000000)
	librt.so.1 => /lib64/librt.so.1 (0x0000003bf3000000)
	libcap.so.2 => /lib64/libcap.so.2 (0x0000003bf7800000)
	libacl.so.1 => /lib64/libacl.so.1 (0x0000003bfd800000)
	libc.so.6 => /lib64/libc.so.6 (0x0000003bf2800000)
	libdl.so.2 => /lib64/libdl.so.2 (0x0000003bf2400000)
	/lib64/ld-linux-x86-64.so.2 (0x0000003bf2000000)
	libpthread.so.0 => /lib64/libpthread.so.0 (0x0000003bf2c00000)
	libattr.so.1 => /lib64/libattr.so.1 (0x0000003c01000000)

LD_LIBRARY_PATH

Library 的路徑可以透過定義 LD_LIBRARY_PATH 變數來指定.

可以直接寫在使用者的 .bashrc 檔案裏.

LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/path/
export LD_LIBRARY_PATH