Linux Fundamentals 8

Access rights:
READ: Allow viewing of content-read
Write: Allow content to be modified-write
Executable: Allow to run and switch-excute
(The above three points rwx together determine the final authority)
Attribution Relationship:
Owner: The user who owns this file/directory-user
Owning group: The group that owns this file/directory-group
Other users: Users other than the owner, the owning group-other
All users: The above three categories belong to collectively-all

Resolve File/directory permissions:
The 8 binary number of the permission bit means: r,w,x corresponds to 4,2,1 respectively, the latter three groups are summed separately
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Group |    User Permissions |    Group Permissions | Other Permissions |
Characters |     R W x |    R-x | R-x |
Digital |     4 2 1 |    4 0 1 | 4 0 1 |
Summation |        7 |       5 | 5 |
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Permissions control:
Set basic permissions: chmod command
Format: CHOMD [ugoa][+-=][rwx] File
chmod [nnn] File
Common Command options:
-R: Recursive Modify permissions

Default permissions for new files/directories
Normal file does not give x Execute permission by default, other depends on umask setting
[Email protected] ~]# umask
0022
[Email protected] ~]# umask-s
U=rwx,g=rx,o=rx (new directory 755, new file 644)

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To set up a attribution relationship:
Owner > Owning group > Other people
Chown command
Format: Chown Master File
Chown: Genus Group File
Chown: The genus Group file (equivalent to the CHGRP command. Specially modified Group)
Common Command options:
-R: Recursive Modify permissions
Operation:
[Email protected]room1pc01 ~]# ls-ld/nsd/
Drwxr-xr-x 2 root root 4096 June 5 13:50/nsd/
[[email protected] ~]# chown anonymous:anonymous/nsd/(modified to Anonymous main Anonymous group)
[Email protected] ~]# ls-ld/nsd/
Drwxr-xr-x 2 Anonymous Anonymous 4096 June 5 13:50/nsd/

[[email protected] ~]# chown root:anonymous/nsd/(modified to root main Anonymous group)
[Email protected] ~]# ls-ld/nsd/
Drwxr-xr-x 2 root Anonymous 4096 June 5 13:50/nsd/

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Special permissions
The U,g,o packet, which is superimposed on the permission bit, is used to pass the program execution identity and restrict directory write rights.

Special Permissions Categories:
The category character indicates that the number represents the overlay position
Set UID s 4 x bit of user
Set GID s 2 x bits of group
Sticky bit T 1 other X-bit
View:
[[Email protected] Desktop]# ls-ld/usr/bin/passwd
-rwsr-xr-x. 1 root root 30768 February 2012/usr/bin/passwd

Set UID
SUID Permissions:
Occupy the X-bit of the owner (User)
Displayed as S or S, depending on whether the owner has X permission
Meaningful only for executable programs
Pass-through owner identity

Set GID
Sgid Permissions:
Occupy the X-bit of the owner (Group)
Displayed as S or S, depending on whether the owner has X permission
Valid for executable program/directory
When other users execute a program with the sgid tag, they have the identity of the program group and the appropriate permissions
In a directory with Sgid permissions, the newly created document automatically inherits the group identity of the secondary directory

Sticky Bit
Sticky Bits,
The X-bit of the other person, shown as T or T, depends on whether the other person has X permission
Applies to directories to restrict user abuse of write rights
In a folder with sticky bits set, you cannot delete or rename other user documents, even if the user has write rights.

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ACL permissions
Ext Series File system support,
Separate RWX permissions can be set for individual users, groups
Set default RWX permissions for a new child profile for a directory
To view ACL permissions:
[[Email protected] Desktop]# tune2fs-l/dev/sda2 |grep ACL
Default Mount Options:user_xattr ACL

Defining ACL control policies
SETFAC command:
Format: setfacl [options] u: User name: Permissions file
setfacl [option] G: Group name: Permission file
Common Command options:
-M: Define an ACL policy
-X: Clears the specified ACL policy
-B: Clears all ACL policies that have been set
-r: Recursive set ACL policy
-D: Set default permissions for the directory (subdocument auto-inherit)

Linux Fundamentals 8