Linux system file permissions setting skills

Windows system is similar to the Linux system, Windows system files, directory properties are read-only, hidden, and Linux is the same.

In Linux, every file has specific properties. It mainly includes two aspects: file type and file permission. There are five different types: normal files, catalog files, linked files, device files, and pipe files.

The so-called file permissions refer to access rights to files, including reading, writing, deleting, and executing files. Linux is a multi-user operating system that allows multiple users to log in and work at the same time. So Linux associates a file or directory with a user or group. The Access Control List (ACL) provides better access control for computers. It is used to restrict access to files, resources, or sockets for all users, including the root user. Here's how to set up a simple setup method.

Step 1 Check the system core

First check if the core of your Linux system has ACL support. Because the Linux system does not have the ability to support ACLs at the core of every version, the easiest way is to check whether the current core of the system can support:

[root@mail /]# cat /boot/config -kernel-version |  Grep -i ext3

CONFIG_EXT3_FS=m

CONFIG_EXT3_IDEX=y

CONFIG_EXT3_FS_XATTR_SHARING=y

CONFIG_EXT3_FS_XATTR_USER=y

CONFIG_EXT3_FS_XATTR_TRUSTED=y< Br>

CONFIG_EXT3_FS_ACL=y

If you can see the above items, it means that it has been compiled into the kernel. The ext3 file system already supports the ACL function. These functions can be found in the compile kernel options. . If you can't find it at compile time, you can go to the ACL's official website to install Kernel (acl.bestbits.at/).

Step 2 Mounting the partition

You can mount the partition and enable the ACL in the following ways:

#mount -t ext3 -o acl /dev/sda1 /fs1

You can also write directly in the /etc/fstab file so that you can support ACL after booting:

#vi /etc/fstab

Step 3 ACL Permissions

ACLs are often set up for individual users. Here are a few different examples:

For example, you need to create test1, test2, and test3 users. You can log in to the system as root first. Then execute the following command to create three usernames and passwords respectively:

[root@mail root]#adduser test1

[root@mail root]#adduser test2

[ ,null,null,3],Root@mail root]#adduser test3

[root@mail root]#passwd test1

[root@mail root]#passwd test2

[root@mail root] #passwd test3

Then mount an ext3 file to the directory /fs1:

[root@mail root]#mount -t ext3 -o acl /dev/sda1 /fs1

Set the file created by test1 to read and write Permissions for test2 :

[root@mail root]#chmod -R 777 /fs1

Allow all users to add files to the directory:

Log in to the system with test1 and execute the command:

[test1@mail test1]# cd /fs1

[test1@mail fs1]# echo "Create by test1" > test1.txt< Br>

[test1@mail fs1]# chmod go-r test1.txt

[test1@mail fs1]# ll test1.txt

-rw------ - 1 test1 test1 17 Jul 14 22:11 test1.txt

The following operations can be used to save test1.txt permissions (except root) except for the read and write permissions of test1. Test2 After logging in to the system, execute the following command:

[test2@mail test2]# cd /fs1

[test2@mail fs1]# cat test1.txt

cat : test1 .txt Permission denied

Then log in to the system with test1 and execute the following command:

[test1@mail fs1]# setfacl -mu:test2:rw test1.txt

Modifying permissions allows test2 to have read and write access to this file. Let's take a look at the changes in its file attributes:

[test1@mail fs1]# ll

-rw-rw-r--+ 1 test1 test1 10 Feb 16 13:52 test1. Txt

will see an additional "+", indicating that the file uses the ACL attribute settings, and then use the command getfacl to view the ACL file attribute settings:

[test1@ Mail fs1]# getfacl test1.txt

# file: test1.txt

# owner: test1

# group: test1

user::rw -

user:test2:rw-

group::rw-

mask::rw-

other::r--

You can see that test2 has permission to read and write this file.

We use test2 to log in to the system and execute the following command to see what happened?

[test2@mail test2]# cd /fs1

[test2@mail fs1]# cat test1.txt

Create by test1

Original test2 You can read the test1.txt file.

[test2@mail fs1]# echo "Modify by test2" >> test1.txt

[test2@mail fs1]# cat test1.txt

Create by test1

Modify by test2

Now test2 can also modify the test1.txt file.

Then log in to the system with test3:

[test3@mail test3]# cd /fs1

[test3@mail fs1]# cat test1.txt

cat : test1.txt Permission denied

嘿嘿, except for test1, test2, no other user has permission to read and write test1.txt (except root).

Although watching it is a little dizzy, in fact, the command is such one or two, mainly to explain the situation to everyone, so that everyone will find in Linux, compared to the vulnerable Windows permissions protection Linux is doing quite well!