ln命令应用

记录：352

场景：在CentOS 7.9操作系统上，使用ln命令创建软链接(symbolic links)和硬链接(hard links)。解决：Too many levels of symbolic links。

版本：

操作系统：CentOS 7.9

1.命令应用

(1)目录创建软链接

命令：ln -s /home/apps/module/jdk1.8.0_281  /usr/java/default

解析：ln -s，创建软链接；目录/usr/java/default是软链接，指向/home/apps/module/jdk1.8.0_281目录；许多软件找jdk会到默认目录：/usr/java/default读取jdk相关数据；创建软链接后，自定义安装目录就满足了需求。创建软链接会有->符号标识。

(2)文件创建软链

命令：ln -s /home/apps/work01/aintro.txt /home/apps/work02/aintro.txt

解析：创建文件软链接，/home/apps/work01/aintro.txt是源文件；另一个是软链接。

(3)创建硬链接

命令：ln -P /home/apps/work01/bintro.txt /home/apps/work02/bintro.txt

解析：创建文件硬链接，/home/apps/work01/bintro.txt是源文件，另一个是硬链接。

2.解决报错

(1)问题一：Too many levels of symbolic links

问题原因：在/home/apps/work01目录下创建软链接，没有使用完整路径。

执行的命令：ln -s cintro.txt  /home/apps/work02/cintro.txt

使用cat命令：cat cintro.txt，读取文件报错，读取不了文件。

解决：先删除有问题的软链接，再重新创建软链接。

删除命令：rm -rf /home/apps/work02/cintro.txt

重新创建命令：ln -s /home/apps/work01/cintro.txt /home/apps/work02/cintro.txt

2.命令帮助手册

命令：ln --help

解析：查看ln支持的全部命令和选项，在实际工作中，查看这个手册应该是必备之选。

Usage: ln [OPTION]... [-T] TARGET LINK_NAME   (1st form)
  or:  ln [OPTION]... TARGET                  (2nd form)
  or:  ln [OPTION]... TARGET... DIRECTORY     (3rd form)
  or:  ln [OPTION]... -t DIRECTORY TARGET...  (4th form)
In the 1st form, create a link to TARGET with the name LINK_NAME.
In the 2nd form, create a link to TARGET in the current directory.
In the 3rd and 4th forms, create links to each TARGET in DIRECTORY.
Create hard links by default, symbolic links with --symbolic.
By default, each destination (name of new link) should not already exist.
When creating hard links, each TARGET must exist.  Symbolic links
can hold arbitrary text; if later resolved, a relative link is
interpreted in relation to its parent directory.
 
Mandatory arguments to long options are mandatory for short options too.
      --backup[=CONTROL]      make a backup of each existing destination file
  -b                          like --backup but does not accept an argument
  -d, -F, --directory         allow the superuser to attempt to hard link
                                directories (note: will probably fail due to
                                system restrictions, even for the superuser)
  -f, --force                 remove existing destination files
  -i, --interactive           prompt whether to remove destinations
  -L, --logical               dereference TARGETs that are symbolic links
  -n, --no-dereference        treat LINK_NAME as a normal file if
                                it is a symbolic link to a directory
  -P, --physical              make hard links directly to symbolic links
  -r, --relative              create symbolic links relative to link location
  -s, --symbolic              make symbolic links instead of hard links
  -S, --suffix=SUFFIX         override the usual backup suffix
  -t, --target-directory=DIRECTORY  specify the DIRECTORY in which to create
                                the links
  -T, --no-target-directory   treat LINK_NAME as a normal file always
  -v, --verbose               print name of each linked file
      --help     display this help and exit
      --version  output version information and exit
 
The backup suffix is '~', unless set with --suffix or SIMPLE_BACKUP_SUFFIX.
The version control method may be selected via the --backup option or through
the VERSION_CONTROL environment variable.  Here are the values:
 
  none, off       never make backups (even if --backup is given)
  numbered, t     make numbered backups
  existing, nil   numbered if numbered backups exist, simple otherwise
  simple, never   always make simple backups
 
Using -s ignores -L and -P.  Otherwise, the last option specified controls
behavior when a TARGET is a symbolic link, defaulting to -P.
 
GNU coreutils online help: 
For complete documentation, run: info coreutils 'ln invocation'

以上，感谢。

2022年11月28日