Some basic commands under Linux, beginners can read, other masters do not need to read:
First, file/dir under linux has three different owners: user, group, and others.
Each type of owner has three kinds of displayed permissions, rwx, and two special permissions of s or t.
rwx is read, write, and execute respectively, the command ls -l file/dir can view the permissions
The general format of the command is:
command [-options] parameter1 parameter2 ......
Command Options Parameter 1 Parameter 2 …
man command: You can view the specific usage of a command and query how its options are used;
like man chown
chgrp [-R] file/dir: change the user group to which the file belongs, -R recursively change, chgrp usersgroup /tmp/test
chown [-R] username file/dir: change the owner of the file
chmod [-R] 777 file/dir: Change the permissions of the file (r for 4, w for 2, x for 1, just add them up)
chmod 755 /tmp/test, set permissions on /tmp/test to rwxr-xr-x
In the use of chown, you can directly chown username:group file/dir, directly modify the file owner and user group, and use " : " to separate;
In the use of chmod, you can also use ugoa to represent users, groups, others, all, -+= to delete, add, set,
For example: chmod a=rwx file/dir; chmod a+w file/dir;
cd dir: switch directories and directly cd back to the current user's home folder
pwd [-P]: Displays the current directory, -P displays the current path, not the link (l) path
mkdir [-mp] dir: create a new directory, -m can directly configure permissions, -p can create an upper directory, mkdir -m 755 /tmp/test
rmdir [-p] dir: delete a directory, -p deletes it together with the upper empty directory (rmdir can only delete empty directories)
PATH="$PATH":dir: configure environment variables, dir is the directory
ls [-options] file/dir: View files or directories. To view specific information, you need to specify different options
ls -l file/fir will appear total in the first line, the unit is k, you can use -h to automatically convert to the appropriate unit, the calculation method is: the actual number of blocks occupied by all data in this directory x the size of the block value,
ls -s can display how many blocks are occupied at the beginning of each line
cp [-options] source dest: copy files or directories, -r will continue to copy recursively, -i will ask when overwriting;
If -a is used, then all attributes of the file are completely copied (), otherwise the attributes and permissions of the executor will be copied
rm [-options] file/dir: delete files or directories, -r can delete recursively
mv [-options] source dest: move file or directory, or rename
nl [-bnw] file: View the file content, -ba displays the line number, including blank lines, -n adjusts the position of the line number, -n ln/rn, -w adjusts the position of the line number -w 3 The first line is displayed as 001
less file: the same as man's display
touch [-acdmt] file: create a file, or modify the time of the file, create a new file when the -c file does not exist, and -dt can specify the time
File time type:
1. The time to update when the mtime content data changes, -m to modify
2. The time that the ctime file permissions or attributes (the attributes displayed by ls -l) will be updated when they are modified.
3. The time that the atime file will be updated when it is read, -a to modify
umask [-S]: The default permission value of the current user when creating a new file or directory, the umask is displayed as 4 digits, and the first one is a special permission
-S is displayed in ugo mode, umask -S is displayed as u=rwx,g=rx,o=rx
The umask directly under root shows 0022, and the ordinary user shows 0002.
Indicates that when creating a file or directory, delete the w permission of the corresponding permission location, (because w corresponds to 2)
Special permissions appear on the x-bit of rwx, such as drwsrwsrwt, if there is no special permission, it should be drwxrwxrwx
According to the different positions of u, g, and o, they are called SUID, SGID, SBIT, (sst), respectively.
SUID: During the execution of the program, the executor will have the authority of the owner (only valid for binary programs)
SGID: You can set files and directories. The executor has the permission of the user group when executing it. When the executor has the w permission of the directory, the user group of the new file created by the user is the same as the user group of this directory.
SBIT: It is only valid for a directory. Only the user and root can delete the files or directories created by the user in this directory.
How to set special permissions:
SUID is 4, SGID is 2, SBIT is 1, which can be set by chmod
chmod 7755 file；chmod 5755 file；
file file/dir: View file types
which [-a] command: script file name (command) query, query in PATH, -a lists all found commands in PATH
whereis [-options] file/dir: file name query, exact match pattern
locate [-ir] keyword: file name query, fuzzy query, -i ignores case, -r can be followed by a regular expression
find [PATH] [-options] [action]: file name query, the following example:
Find the files between 50k-60k under /etc, and list the permissions
find /etc -size +50k -a -size -60k -exec ls -ld {} \;
The meaning of permissions to files:
r: the content of this file can be read
w: can edit, add or modify the content of the file
x: the file has permission to be executed by the system
The file does not have the permission to execute x by default (rw-rw-rw), and the umask is also integrated to assign the permission when it is created.
For example, the file permissions created by root are: rw-r--r--, and those created by users are rw-rw-r--
The meaning of permissions for directories:
r: Indicates the permission to read the directory structure list, (ls)
w: permission to add or delete files or directories, or permission to rename files or directories, and permission to transfer file or directory locations
x: represents whether the user can enter the directory to become the working directory, (cd)
The default permission of the directory is rwxrwxrwx, and the umask should be integrated to assign the permission when it is created.
For example, the directory permissions created by root are rwxr-xr-x, and those created by users are rwxrwxr-x