Special permissions and links

The fourth class in two weeks (Aug. 10) 2.18 Special permission set_uid

2.19 Special permission set_gid

2.20 stick_bit2.21 soft link files with special permissions

2.22 hard link file

2.18 Special permission set_uid

An ordinary user has temporary owner permissions (binary files)

Ls / root not allowed

Chmod Utility / usr/bin/ls

Chmod Umurs / usr/bin/ls

If the user does not have x permission, it becomes S, just like s, but does not have the permission to execute.

2.19 Special permission set_gid

For files, the user is temporarily granted permission to the user group during execution

For a folder, the new files created under this folder belong to the same group as the subordinate group of the folder.

2.20 Special permission stick_bit

Ll-d / tmp

For folders with t at the end of the other bit, files of other users cannot be deleted between different users, and can only be modified.

Note:

For files: (the following test of file permissions is in the case of 777 in the upper directory)

Readable: indicates that the contents of the copied file can be read

Writable: indicates that the contents of the file can be modified

Executable: indicates that operations can be performed on files with other parsers

The deletion of files is determined by the upper directory

For folders:

Readable: indicates that you can list the directory itself and the files and folders under the directory

Writable: it means you can write files or folders to the directory.

Executable: indicates that you can read or overwrite the contents of the file under the directory

Writable only: no execute permission, just like no write permission.

2.21 soft link file

A shortcut similar to Windows.

Put the files that need to be connected by the software first.

The software can connect the file to the directory.

If you are making a soft connection in the current directory, ll displays the relative path. When creating a soft connection, try to use an absolute path.

Example analysis: the file 1.log under / dev/sda is full and the disk / dev/sdb is empty. You can 1.cp 1.log under the dev/sdb mount point, 2. Delete the location under the 1.log 3.ln-s 1.log XXX xxx representation / dev/sdb.

2.22 hard link file

Only hard links to files are supported.

Ln 1.txt 2.txt

Properties:

Same number as inode.

Delete any file and the other file still exists

Cannot cross partitions.