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Sort Sorts lines of text files by default, non-numeric. sort - sort lines of text files Reverse Order sort -r file Numeric Sort sort -n file Sort By Month Month format: Jan, Feb, Mar. sort -M file Specify Column Default is separated by (consecutive) space...

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Full name Global Regular Expression Print, originated from a Unix editor ed command g/re/p, where g (global) is global matching, re (regular expression) is regular expression, p (print) is print. Therefore, the grep tool is essentially used to globally match r...

PS stands for Process Status. man ps ps - report a snapshot of the current processes. Style Source Prefix Unix AT&T System of Bell Labs - BSD Berkeley Software Distribution None GNU Improved version by GNU Project -- Due to historical reasons, ...

Kill Command It's actually a tool for sending signals to processes, not necessarily killing them. man kill kill - send a signal to a process Default Signal The default signal for the kill command is SIGTERM, corresponding to number 15, for a graceful termin...

man top top - display Linux processes The top command defaults to sorting processes by CPU usage rate and dynamically displaying the results. top - 09:19:05 up 6 days, 10:02, 2 users, load average: 0.13, 0.05, 0.01 Tasks: 126 total, 1 running, 125 sleepi...

Origins The environment variables in Linux originated from the design requirements of early UNIX systems. Through environment variables, users and processes can dynamically influence system behavior without modifying the system's core code. This flexibility a...

Shebang is a special symbol in Unix and Unix-like operating systems, composed of the characters #!, used to indicate which interpreter should execute a script file. It usually appears at the beginning of a script file, followed by the path of the interpreter. ...

Startup Methods The startup methods of Shell will affect the loading process of environment variables, which can be divided into the following categories. Interactive (Interactive) Login: Shell instances started in login mode, such as SSH login. Non-login: ...

SHELL The current shell in use. printenv SHELL /bin/bash HOME The path to the user's home directory. printenv HOME /home/kuga PWD The path to the current directory. printenv PWD /home/kuga USER The current user. printenv USER kuga PATH The path wh...

File System Types You can use the -T option of the df command to view the Type field. df -Th Filesystem Type Size Used Avail Use% Mounted on tmpfs tmpfs 168M 1.1M 167M 1% /run /dev/vda3 ext4 40G 3.2G 35G 9% / tmpfs ...

Access Control List (ACL) is a more flexible and fine-grained permission management mechanism, used to define and control the access permissions of file system objects. Compared to traditional file permission systems, ACL provides more detailed permission cont...

Composition Structure -rwxr-xr-- The first character indicates the file type: -：File, such as text files, binary files, etc. d：Directory. l：Symbolic link, Symbolic link (Soft link). b：Block device, such as hard disk, CD-ROM, etc. c：Character device, such as...

Relationship Primary Group When a user is created, a group with the same name is also created, which is the primary group. grep soda /etc/passwd soda:x:1001:1001:,,,:/home/soda:/bin/bash The fourth field indicates the primary group ID 1001, which can also b...

Account /etc/passwd Linux uses the /etc/passwd file to store user account information. Because many service processes need to read user account information, you can see that the file's permissions are all readable. -rw-r--r-- 1 root root 2010 Aug 24 15:12 /et...

Basic Concepts A file descriptor (FD) is an integer identifier used to represent an open file or other input/output resources in an operating system. It serves as a bridge between the operating system and applications for file operations. In Linux, a file des...

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Basic Concepts A pipe can use the output of one command as the input of the next command, represented by the symbol | in the command-line environment, which is a form of one-way communication between processes, implemented based on file descriptors. Working ...

The first process of the system, with a process ID of 1. ps -p 1 PID TTY TIME CMD 1 ? 00:00:04 systemd However, when we want to display detailed information, the result will be different. ps -p 1 -f UID PID PPID C STIME TTY TIME CMD r...