Basic Linux commands

May 9, 2021 • 8 minutes read

Navigation

Command	Description
cd /var/www	go to the /var/www folder
cd ..	go to the folder one level above
cd ../..	go on 2 levels higher than the current directory
cd	go to the home folder
cd ~john	go to the john's home folder
cd -	go to the directory in which you were before switching to the current directory
pwd	show the path to the current directory
ls	display the contents of the current directory
ls -lh	print a detailed list of files and directories in the current directory
ls -a	show hidden files and folders in the current directory

Managing Files and Folders

Сommand	Description
mkdir dir1	create a directory with the name dir1
mkdir dir1 dir2	create 2 directories with the names dir1 and dir2
mkdir -p /tmp/dir1/dir2	create directories recursively
rm -f file1	remove file with the name file1
rmdir dir1	remove directory with the name dir1
rm -rf dir1	delete the directory named dir1 and recursively all its contents
rm -rf dir1 dir2	delete two directories and recursively their contents
mv dir1 new_dir	rename or move a file or directory
cp file1 file2	copy file file1 to file file2
cp dir/* .	copy all files in the dir directory to the current directory
cp -a /tmp/dir1 .	copy directory dir1 with all contents to the current directory
cp -a dir1 dir2	copy directory dir1 to directory dir2
ln -s file1 lnk1	create a symlink to a file or directory
ln file1 lnk1	create a "hard" link to a file or directory

Text files

Command	Description
cat filename.txt	show content from filename.txt
tail /var/log/syslog -n 5	show last 5 records from the end of the file
head /var/log/syslog -n 5	show first 5 records from the begging of the file
nano filename.txt	edit filename.txt
touch -t 0712250000 filename.txt	modify the creation date and time of an existing file or create a file with the specified date and time (YYMMDDhhmm)

Permissions

Permissions represented as numbers. Each number shows access level

Number	Permission	Text representation
0	No permission granted	---
1	Can execute	--x
2	Can write	-w-
3	Can write and execute (2 + 1 = 3)	-wx
4	Can read	r--
5	Can read and execute (4 +1 = 5)	r-x
6	Can read and write (4 + 2 = 6)	rw-
7	Can read and write and execute (4 + 2 + 1 = 7)	rwx

The various owners can be represented as one symbol in Linux

Symbol	Description
u	user (owner)
g	group
o	other
a	all

Command	Description
chmod g+w file.txt	add write access for group
chmod g-w file.txt	remove write access for group
chmod +w file.txt	add write access for all
chmod g+x test.sh	add execute access for group
chmod 000 secret-file.txt	no permissions granted for all
chmod 754 test.sh	Owner can read and write and execute. Group can read and execute. Others can read only
chmod 777 /var/test/ -Rf	Add full permissions for all recursively

Script and program execution

Command	Description
./script.sh	run script.sh from current user from current directory
sudo ./script.sh	run script from root user
sudo -u www-data whoami	run command whoami from www-data user
sudo -i	run another terminal session from root user

Process control

Сommand	Description
ps -auxf	display running processes
pstree	display the process tree
kill -9 98989 or kill -KILL 98989	"kill" the process with PID 98989 "to death" (without observing data integrity)
kill -TERM 98989	correctly terminate the process with PID 98989 by sending a TERM signal to it
kill -1 98989 or kill -HUP 98989	send a signal to re-read the configuration file to the process with PID 98989

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