Commands and permissions for directories and files

1 Directory command

• Directory switching

cd 
cd /  // Switch to the root directory 
cd ..   // Go back to the previous Directory 
cd ~   // Return to your home directory 
cd -   // Return to the upper level directory 

• Catalog view

pwd   // View the current directory path 

ls     // View the directory under the current directory 、 file 
ls -l  // View the detailed directory under the current directory 、 file 
ls -i  // View the directory under the current directory 、 Document number 
ls -lh // View the directory under the current directory 、 File size 
ls -a  // Display all files 
ls -ld // Look at the catalog itself 

• Create directory

mkdir  a  // establish  a  Catalog 
mkdir -p  dir1/dir2/a  // If there is no  dir  Catalog , be  -p  Automatically create 

• duplicate catalog

cp -r dir1 dir2       // Copy  dir1  In the same directory , name  dir2
cp -r dir1 dir2  dir3  // Copy  dir1 dir2  To  dir3  Under the table of contents 

• Mobile directory

mv dir1 dir2  // If  dir2  non-existent , amount to  dir1  rename  dir2
mv dir1 dir2  dir3 // If  dir3  There is ,dir1  and  dir2  Move to  dir3

• Delete directory

rm -r a  // Delete  a  Catalog 
rm -rf a b c // Forced deletion of included files and directories 

• System catalog

Directory name	effect
/boot	System boot directory ,Liunx Startup time , Required documents such as ： Kernel files and boot loader files
/dev	Device file , Hardware file
/etc	The configuration file , Script files
/home	The root directory where all user files are stored , Is the base point of the user's home directory , Such as user user The home directory of /home/user, It can be used ~user Express
/root	Administrator home directory
/proc	Virtual file system saved to memory . Save the kernel of the system , process , External device status and network status lights . Such as /proc/cpuinfo Is save CPU The information of ,/proc/devices yes To save a list of device drivers ,/proc/filesystems Is to save the list of file systems ,/proc/net yes To save network protocol information
/sys	Virtual file system . and /proc The catalog is similar to , It's all stored in memory , It is mainly stored in kernel related information
/srv	Service data directory .- - After some system services are started , You can save the required data in this directory
/tmp	Temporary directory . The directory where the system stores temporary files , All users in this directory can access and write
/usr	System software resource directory . yes “Unix SoftwreResource” Abbreviation , It is the directory where the system software resources are stored . Most of the software installed in the system is stored here ,
/var	Dynamic data storage location . Mainly save cache 、 Logs and files generated by software operation
/media	Mount Directory . System recommendations are for mounting media devices , For example, floppy disks and compact disks
/mnt	Mount Directory , In the early Linux There is only one mount directory in the , There is no subdivision . Now the directory system recommends mounting additional devices , Such as U disc , Partition of mobile hard disk and other operating systems
/opt	Storage location of software installed by a third party . This directory is where other software is placed and installed , I manually install the source code package software can be installed into this directory . But I'm still more used to putting software in /usr/loca1/ Directory of , in other words /usr/local/ Directories can also be used to install software
/run	Process documents
/bin	Directory where system commands are stored , Common users and super users can execute . But put it on /bin’ The command under can also be executed in single user mode
/ sbin	Save commands related to system environment settings , Only the super user can use these commands to set the system environment , But some commands allow ordinary users to view
/usr/bin	Directory where system commands are stored , Common users and super users can execute . These commands have nothing to do with system startup , Cannot execute in single user mode
/usr/sbin	Store unnecessary system management commands for the root file system , For example, most service programs . Only super users can use . You can actually notice Linux The system of , In all “sbin" The commands saved in the directory can only be used by super users ,“bin” The commands saved in the directory are available to all users
/usr/lib	32 Location files
/usr/lib64	64 Location files

2 File command

2.1 File base commands

• create a file

touch file1

• see file

ls     // View the directory under the current directory 、 file 
ls -l  // View the detailed directory under the current directory 、 file 
ls -i  // View the directory under the current directory 、 Document number 
ls -lh // View the directory under the current directory 、 File size 
ls -a  // Display all files 
ls -ld // Look at the catalog itself 

• Copy file

cp file1 file2      // Copy  file1  In the same directory , name  file2
cp file1 file2  dir  // Copy  file1 file2  To  dir  Under the table of contents 

cp -p  // Moving files , And save all the original information 

• Move （ rename ） file

mv a b      // Move to local , And renamed  
mv a b dir // hold  a,b  Move to  dir  Catalog 

• Delete file

rm a b c  // Delete normal files 
rm -f a b c // Force file deletion 

General account rm Deleting does not prompt ,
root Prompt for administrator to delete ,y yes n no
Unless -f Mandatory deletion , Use caution

2.2 The command to view the contents of a file

1. cat

cat file  // View the contents of the file in positive order 
tac file  // Check the contents of the file in reverse order 
cat -b file  // The file content displays the line number 

cat -A file  
// View hidden content ： A newline 、 Space 、 Special symbols 

2. nl

nl -ba file // Whether there is an empty line or not , Line numbers are listed 
nl -bt file // If there is a free line , Line numbers are not listed 

3. less

less file

/           To find the character 
:f          Displays the file name and number of lines 
b           Turn to the first page 
 Space         Page down 
pagedown    Page down 
pageup      Page up 
q           sign out 

4. head、tail

head file  // Display the first ten lines of the file 
tail file // Show the last few lines of the file , Generally, check the log （ dynamic ）

 Parameters 
-n： Show a few lines （ Default ten rows ）
-f： Dynamic display at the end of the file 

5. wc

wc -l  file name   // Display row number 
wc -c  file name  // Display bytes 

2.3 lookup 、 Replace the contents of the file

• grep

Can only be used to find the contents of a file

grep -i Happy file

 Parameters 
-i ： View includes Happy All the lines of this word 
-v ： View does not contain Happy All the lines of this word 
-n ： Match to Happy The content of the line shows the line number 
-c ： see Happy There are several lines of this word 

sed Can find , Then replace or insert what you want

character	Means
a	newly added ,a You can use a string after , And these strings will appear on a new line ( The next line at the moment )
d	Delete , Because it's deletion , therefore d Usually there's nothing to take back ;
i	Insert ,i You can use a string after , And these strings will appear on a new line ( The current line );
p	Print , It is also about to print the selected information . Usually p And parameters sed.
s	replace , Work that can be replaced directly !

• Find files find

 usage :find[ route ][ Command parameter ][ expression ]

 Parameters :
-name “ file name ”： Find the file with the specified name ;
-user： Find files owned by the specified user ;
-group： Find the files owned by the specified group ;
-mtimen： Find in N A document that was modified two days ago ;
-atimen： Find in N The files that were accessed a day ago ;
-type d/t/b/1/p： Find another piece of the specified type ;
-empty： Find empty files ;
-size： Search by capacity ;
-perm mode： Find the file with the specified properties ;
-exec command{
    } \： Find the specified file and execute the specified command ;
-newer file name ： Find a file newer than the specified file 

find *   // All characters 
find ？  // Single character 

• Look up the directory which

which  command 

2.4 Soft connection 、 Hard links

Hard links ：

1. and cp -p The same meaning , however Hard links Can be updated synchronously
2. You cannot hard link directories ,
3. No zoning

ln
ln -l

Soft connection

ln -s： Soft connection 

3 File and directory permissions

3.1 Query authority

ls -l Query details , What does each place mean

• type

d Presentation directory
– Said file
1 Express Connection file
b Represents a device file , Interface device providing storage
c Represents a device file . Provide serial interface device – keyboard ,

• jurisdiction

rwx, read 、 Write 、 perform , No authority is -
The first group rwx ： file owner Authority
Second group rwx ： file Subordinate to the group Authority
The third group rwx ： file others Authority

1. File permissions

The owner of the file is the user , No, w Permissions can also be forced to write ！. The group and others do not .

r： View file contents
w： Can write
x： Sure vim edit

2. Directory permissions :

The user does not have a directory w Authority , You can edit the files in this directory owned by you

r： Check the files in the directory
w:

1. You can create new files and directories in this directory
2. You can delete existing files and directories
3. Rename existing files and directories
4. Move the location of files and directories in this directory

x： Can I enter this directory

3.2 Modify the permissions

• chmod modify The owner and Subordinate to the group Authority

1. Digital method ：r=4,w=2, x=1

chomd 777 123
// 123 The owner of the 、 Subordinate to the group 、 The authority of others is  rwx-rw-rw-

2. Addition and subtraction

The owner / Subordinate to the group / others ,u / g / o , + / - / =,r / w / x

chomd u=rx 123// 123 The owner permission of is  rx
chomd u+w 123 // 123 The owner permission of is  rwx

• chown Modify the owner

chown  root  abc  // modify  abc  The owner of is  root
chown  -R root  abc  // Recursive modification  abc  The owner of is  root
//abc  All owners of the directory are changed to  root

• chgrp Modify group

groupadd  Group name   // New group 

gpasswd -a  user   Group name  // Field users are grouped 

chgrp  root  abc  // modify  abc  Is a member of  root
chgrp  -R root  abc  // Recursive modification  abc  Is a member of  root
//abc  All groups contained in the directory are changed to  root

4 Default permissions

• umask： View the default permissions for the current user to create files and directories

0022： Represents the authority taken away
first 0： On behalf of special authority
022：rwxr-xr-x

When creating files and directories , Will take away the file by default x jurisdiction

1. Temporarily modify the default permissions

umask 000  
// When creating files and directories , file rw-rw-rw-, Catalog rwxrwxrwx

2. Permanently change the default permissions （ Not recommended ）

/etc/bashre // Modify the value inside

5 Special privileges

drwxrwxrwt. 14 root root 4096 10 month 23 19:32 / tmp/
rwsr- xr-x .1 root root 27832 6 month 10 2014 /usr/bin/ passwd

When s Appear in the owner's x Permission position , Indicates that the owner has SUID Authority (Set UID)
When s Appears in the x Permission position , Indicates that the group has SGID Authority (Set GID)
When t Appear in other people's x Permission position , It means that others have SBIT Authority (Sticky Bit)

1. SUID, Temporarily obtain the permission of the file owner only for the file
2. SGID, Even if it can work on the directory , It can also act on files
   Act on documents : SUID equally
   Works on the catalog : Inherit the instrument set directory a directory will continue to inherit
3. SBIT refer to , Only the owner of the file can delete 、 Modify the files in this directory .
   Only for directory
   And it can only be modified in the position of others

S and T There are upper case and lower case
Capitalized description : No, x jurisdiction
Lower case description : Yes x jurisdiction .

• SUID

1. Only executable binary programs can be set SUID jurisdiction
2. The command executor should have x ( perform ) The authority command executor obtains the identity of the owner of the program file when executing the program ( In the process of executing the program, the soul is attached as the owner of the document )
3. SetUID Permission is only valid during the execution of the program , That is to say, identity change is only effective in the process of program execution

When it comes to execution , Temporary possession SUID jurisdiction

• SGID

1、 For documents

1. Only executable binaries can be set SGID jurisdiction
2. The command executor should have x Executive authority
3. Command execution is when executing a program , The group identity is upgraded to the group of the program file
4. SetGID Permission is also only valid during the execution of the program , That is to say, group identity change is only effective during program execution

2、 For catalog

1. Normal users must have and for this directory x jurisdiction , To access this directory
2. The effective group of ordinary users in this directory will become the subordinate group of this directory
3. If the average user owns this directory w Authority , The default group of the new file is the group of this directory

• SBIT

1. The glue bit is currently only valid for directories
2. Ordinary users have w and x jurisdiction , That is, ordinary users can have write permission in this directory
3. If there is no adhesive position , Because ordinary users have w jurisdiction , So you can delete all files in this directory , Include files created by other users . But it gives an adhesive bit , except root All files can be deleted , Ordinary users even have w jurisdiction , You can only delete your own files , But you can't delete files created by other users

• Modify special permissions

Digital method ：SUID=4 SGID=2 SBIT=1

chomd 4777  file name  
chomd 2777  file name  
chomd 1777  Directory name  

chmod u+s  file name 
chmod g+s  file name 
chmod o+t  Directory name 

• Delete special permissions

chmod 777  file name 

chmod u-s  file name 

6 ACL File permissions

If a user in the system has permission to write to a file , But this user belongs to other, It can only be opened other Authority . But once open other Authority , every last other Can access this file ,

file ACL Permission solves this problem
acl: For a single user , Set up a single file or directory to rwx Permission modification of

• Set the acl jurisdiction setfacl

setfacl -m u: Account name : rwx  file name / Directory name 
// This file / Catalog   Joined the acl jurisdiction , With a specific account 
setfacl -m g:  Group name : rwx  file name / Directory name 

setfacl -m m: rwx // modify mask value 


 Parameters 
-m： To configure acl Parameters 
-x： Delete a single file acl
-b： Delete acl Configuration of 
-R： Recursive configuration ac Parameters 

• Delete acl

setfacl -x u: Account name   file name / Directory name 

setfacl -x g: Account name   file name / Directory name 

setfacl -b  file name / Directory name   // Delete all of the files  acl jurisdiction 

• recursive ACL jurisdiction

setfacl -m u: Account name : rwx -R  Directory name  

• Default ACL jurisdiction

setfacl -m d:u: Account name : rwx  Directory name  

• Look at the file acl jurisdiction getfacl

getfacl  file name / Directory name 

• Maximum effective permissions mask

mask The definition of ,acl Permission limit
1、mask by Set up acl file / Catalog Maximum valid permissions for
2、 Needs and settings acl jurisdiction Meet each other Get permission , That's the file / The directory is really acl jurisdiction

7 File system hidden properties

A lock prevent root Users including users , Misoperation of documents

i： If the file is set i attribute , Deleting files is not allowed 、 Change of name , You can't add or modify data ; If the directory is set i attribute , Then you can only modify the data of files in the directory , But it's not allowed to create and delete files .
a：
If the file is set a attribute , Then you can only add data to the file , But you can't delete or modify data ; If the directory is set a attribute , Only files can be created and modified in the directory , But deleting... Is not allowed

• Set file hiding properties chattr

chattr +i  file name / Directory name 
chattr -i  file name / Directory name 
chattr =i  file name / Directory name 

• View file hidden properties lsattr

lsattr

 Parameters 
-a： Show all files and directories 
-d： If the target is a directory , Show only the directory itself , Not a sub file 

8 sudo jurisdiction

The shutdown command can only root The user to use , however root User is too busy , It can be given to ordinary users

1. root Assign commands that can only be executed by super users to
2. Common user execution .sudo The object of operation is the system command , The system command is also a file

• View the permissions granted

sudo -l

• Set up sudo

visudo   // What is actually modified is /etc/sudoers file 

• Example

visudo

SC ALL= /sbin/shutdown -r now // to sc The user grants restart permission 	

sudo /sbin/ shutdown -r now // Ordinary users perform the given permissions