Ldconfig command

Reference resources   ldconfig command - cloud + Community - Tencent cloud

Catalog

1、 brief introduction

2、 Command format

3、 Parameter description

4、 Common examples

5、 matters needing attention

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1、 brief introduction

ldconfig The command is mainly used to search the default directory /lib and /usr/lib And dynamic library configuration files /etc/ld.so.conf Under the directory listed in , Search for shared dynamic link libraries （ The format is as follows lib*.so*）, And then create a dynamic linker （ld.so or ld-linux.so） Required cache files . The cache file defaults to /etc/ld.so.cache, This file holds an ordered list of DLL names , In order to make the DLL shared by the system , Need to run dynamic link library management command ldconfig Update the cache file of the dynamic link library , This executive program is stored in /sbin Under the table of contents .ldconfig Usually run at system startup , When a user installs a new DLL , You need to run this command manually .

2、 Command format

/sbin/ldconfig [ -nNvXV ] [ -f conf ] [ -C cache ] [ -r root ] directory ...
/sbin/ldconfig -l [ -v ] library ...
/sbin/ldconfig -p

3、 Parameter description

-v, --verbose
	 With this option ,ldconfig  The directory being scanned and the DLL being searched will be displayed , And the name of the link it creates 

-n
	ldconfig Scan only the directories specified on the command line , Do not scan the default directory （/lib、/usr/lib）, Also do not scan the configuration file  /etc/ld.so.conf  List of directories .

-N
	ldconfig  Do not rebuild cache files （/etc/ld.so.cache）, If not  -X  Options ,ldconfig  Update the file link as usual 

-X
	ldconfig  Do not update file links , If not  -N  Options , The cache file is rebuilt as usual 

-f <conf >
	 Specify that the configuration file of the dynamic link library is  <conf > , The system defaults to  /etc/ld.so.conf

-C <cache>
	 Specify that the generated cache file is  <cache>, The system defaults to  /etc/ld.so.cache, This file holds a sorted list of shareable dynamic link libraries 

-r <root>
	 Change the root directory of the application to  <root>（ Is to call  chroot  Functionally implemented ）. When this option is selected , System default profile  /etc/ld.so.conf, The actual correspondence is  <root>/etc/ld.so.conf. If used  -r /usr/zzz when , Open profile  /etc/ld.so.conf  when , What is actually opened is  /usr/zzz/etc/ld.so.conf  file . With this option , It can greatly increase the flexibility of dynamic link library management 

-l
	 Usually ,ldconfig  The dynamic link library will be automatically linked when searching the dynamic link library , When this option is selected , Will enter expert mode , You need to set the link manually , General users do not need this item 

-p, --print-cache
	ldconfig  Print out the names of all shared libraries saved in the current cache file 

-c FORMAT  or  --format=FORMAT： This option is used to specify the format used by the cache file , There are three kinds ：old( Old format ),new( New format ) and compat（ Compatible formats , This is the default format ）.

-V
	 Print out  ldconfig  Version information for 

-?, --help, --usage
	 These three options work the same , It's all about letting ldconfig Print out its help information 

4、 Common examples

（1） Show ldconfig Help information .

ldconfig -?

（2） Show ldconfig Version information .

ldconfig -V

（3） Refresh the dynamic link library cache file /etc/ld.so.cache.

sudo ldconfig

5、 matters needing attention

（1） Go to /lib and /usr/lib Add dynamic link library inside , No need to modify /etc/ld.so.conf Of , But after that, we need to adjust it ldconfig, Otherwise, this library Will find .

（2） When you want to add something to the above two catalogues , Be sure to revise it /etc/ld.so.conf, Then call ldconfig, Otherwise, it will not be found .

Like installing a mysql To /usr/local/mysql,mysql There's a lot of library stay /usr/local/mysql/lib below , And that's where we need to be /etc/ld.so.conf Add a line to it /usr/local/mysql/lib, Execute after saving ldconfig Update the dynamic link library cache /etc/ld.so.cache, new library Can be found when the program is running .

（3） If you want to /lib and /usr/lib These two directories are placed outside lib, And I don't want to /etc/ld.so.conf Directory of China Canada dynamic link library （ Or without permission ）. Then you can. export A global variable LD_LIBRARY_PATH, Then when you run the program, you will go to this directory to find library. Generally speaking, it's just a temporary solution , Use it when you don't have permission or need it temporarily .

（4）ldconfig Updating the cache file of the dynamic link library is only related to the program runtime , It has nothing to do with compile time . Compile with -L You have to add , Don't confuse .

（5） All in all , No matter what you do about library After the change , Better all ldconfig once , Otherwise, there will be some unexpected results . It won't take much time , But it will save a lot of things .