/usr/bin/ld: warning: **libmysqlclient. so. 20**, needed by //usr/

Error message

/usr/bin/ld: warning: libmysqlclient.so.20, needed by //usr/lib/libgdal.so.20, not found (try using -rpath or -rpath-link)
//usr/lib/libgdal.so.20： Yes ‘[email protected]_20.0’ Undefined references
//usr/lib/libgdal.so.20： Yes ‘[email protected]_20.0’ Undefined references
//usr/lib/libgdal.so.20： Yes ‘[email protected]_20.0’ Undefined references
//usr/lib/libgdal.so.20： Yes ‘[email protected]_20.0’ Undefined references
//usr/lib/libgdal.so.20： Yes ‘[email protected]_20.0’ Undefined references
//usr/lib/libgdal.so.20： Yes ‘[email protected]_20.0’ Undefined references
//usr/lib/libgdal.so.20： Yes ‘[email protected]_20.0’ Undefined references
//usr/lib/libgdal.so.20： Yes ‘[email protected]_20.0’ Undefined references
//usr/lib/libgdal.so.20： Yes ‘[email protected]_20.0’ Undefined references
//usr/lib/libgdal.so.20： Yes ‘[email protected]_20.0’ Undefined references
//usr/lib/libgdal.so.20： Yes ‘[email protected]_20.0’ Undefined references
//usr/lib/libgdal.so.20： Yes ‘[email protected]_20.0’ Undefined references
//usr/lib/libgdal.so.20： Yes ‘[email protected]_20.0’ Undefined references
//usr/lib/libgdal.so.20： Yes ‘[email protected]_20.0’ Undefined references
//usr/lib/libgdal.so.20： Yes ‘[email protected]_20.0’ Undefined references
//usr/lib/libgdal.so.20： Yes ‘[email protected]_20.0’ Undefined references
//usr/lib/libgdal.so.20： Yes ‘[email protected]_20.0’ Undefined references
//usr/lib/libgdal.so.20： Yes ‘[email protected]_20.0’ Undefined references
//usr/lib/libgdal.so.20： Yes ‘[email protected]_20.0’ Undefined references
//usr/lib/libgdal.so.20： Yes ‘[email protected]_20.0’ Undefined references
//usr/lib/libgdal.so.20： Yes ‘[email protected]_20.0’ Undefined references
collect2: error: ld returned 1 exit status
line_det/CMakeFiles/line.dir/build.make:167: recipe for target ‘/home/dzh/Demo/line_det/devel/lib/line_det/line’ failed
make[2]: *** [/home/dzh/Demo/line_det/devel/lib/line_det/line] Error 1
CMakeFiles/Makefile2:455: recipe for target ‘line_det/CMakeFiles/line.dir/all’ failed
make[1]: *** [line_det/CMakeFiles/line.dir/all] Error 2
Makefile:140: recipe for target ‘all’ failed
make: *** [all] Error 2
Invoking “make -j12 -l12” failed
Terminal process “bash ‘-c’, ‘catkin_make’” Terminated , Exit code : 1.

resolvent

After an afternoon 3h The fumble of , Finally solved the above problems . To sum up, let the scholars behind take fewer detours . The reason for the error is that the system cannot find libmysqlclient.so.20 This library .

1、 So let's start with Ubuntu Find out whether there is this file in the system .
Input find / -name libmysqlclient.so.20. If there is, it will be in /usr/local/mysql/lib/ Medium or /usr/lib/mysql/plugin in , Install it on your own mysql From the path of .

2、 If you have this file , Direct section 3 Step . Without this library , Open the following Baidu online link , Then download to local . Switch to the download directory , Then input sudo mv libmysqlclient.so.20 /usr/lib/mysql/plugin Move library files to mysql/plugin in .

3、 Now we have this library file , We need to set a soft link to the file name required by the system libmysqlclient.so.20. such , As long as the system wants to access libmysqlclient.so.20, Will call this library file . You can regard the soft connection as a reference to a file , The specific explanation is at the end of the text .

Enter the command ：sudo ln -s /usr/lib/mysql/plugin/libmysqlclient.so.20 /usr/lib/libmysqlclient.so.20 Press enter to enter the administrator password , Then create successfully . If you input wrong, you want to delete the soft link , Input rm -rf /usr/lib/libmysqlclient.so.20 You can delete , That is to say rm -rf Link pathname .

4、 Let's compile the project again , If it's in VsCode Medium , direct Ctrl+Shift+B, Compile successfully .

stay Linux In the system , The kernel allocates one for each newly created file inode( Index node ), Each file has a unique inode Number . The file properties are stored in the index node , When accessing a file , The index node is copied to memory , So as to achieve rapid access to files .
A link is a way to establish a connection between a shared file and several directory entries of the users who access it .Linux There are two types of links in ： Hard links (Hard Link) And soft links (Soft Link), Soft links are also called symbolic links （Symbolic link）, amount to Windows Next shortcut .