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# 1  
Parent directory ".."


I know in liunx "." is currect directory and ".." is for parent directory.But if go to (/) directory and give "ls -a", could see "." (denotes current direcctory) and ".." Really don't know why ".." present under (/) directory.

[root@xxxxxx /]# pwd
[root@xxxxxx /]# ls -a
.             boot           lib         etc      test
..            dev            lib64

# 2  
Originally Posted by stew
Really don't know why ".." present under (/) directory.
This is a bit unintuitive, but in fact it comes from the structure of the filesystem itself. Filesystems in UNIX (any UNIX filesystem i know so far) rely on "inodes", which hold the files metadata (creation date, size, owner, ...). These metadata are organized in always the same way for any "file" type there is: file, directory, FIFO, block device, character-device and link.

Because "/" is a directory (like any other directory) there is an entry in the data structure with the parent directory and it has to be filled. In any non-root directory this is a directory different of the directory the inode belongs to, i.e. in the inode of a directory "/some/where/dir" the entry for the parent directory will read "/some/where". In case of the root-dir this will point to root ("/") itself.

You can test this by:

# cd /
# pwd
# cd ..
# pwd

Note, that a "cd .." does not lead to an error, so there is indeed a parent directory to "/" - which is "/" itself.

I hope this helps.

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