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Linux Essential Commands

man: manual page.
- Explains how to use a shell command.
- man <COMMAND>: For example, to find out how to use man, type man man
ls: list directory content
cd: change directory
pwd: print working directory
wc: count word, line, character, and byte
head: display first 10 lines of a file
tail: display the last part of a file
cat: concatenate and print the file
more: display output one screen at a time
cp: copy file
- cp <SOURCE> <DESTINATION>
mv: move file (can be use as changing file name)
- mv <SOURCE> <DESTINATION>
rm: remove file (like delete)
- rm -r: remove directory (like rmdir)
chmod: change file modes or Access Control Lists
- (u,g,o): user, group, other
- (r,w,x): read, write, execute
chown: change file owner or group
mkdir: make directories
rmdir: remove directories
ssh: OpenSSH SSH client (remote login program)
- ssh usrname@ip_adress
scp: secure copy (remote file copy program)
- scp <SOURCE> USRNAME@IP:<DESTINATION>
- scp USRNAME@IP:<SOURCE> <DESTINATION>
- -p: 保留原始檔案權限＆修改日期等, -r: 複製整個資料夾
2>&1: send STDERR to STDOUT (0:STDIN, 1:STDOUT, 2:STDERR)
&: running job in background (終端機背景執行)
nohup: 系統背景執行（不同於&）
- nohup <COMMAND> &
free -g: 查看實際剩餘ram（單位為G）
grep: find keywords in file
- grep <KEYWORD> <FILENAME>
nice and renice: run a program with modified priority. If the server is under heavy load and you need to start a non-urgent large job, please use these.