Linux Command

cmd --help
cmd -h
man cmd
man -k search_term
which cmd
history |tail -10
history |grep keyword
!!
!-2

cd ..
cd -
pwd
xdg-open .

ls -l  # details
ls -a  # hidden
ls -F  # file type
ls -t  # sort by modified time
ls -r  # reverse
ls -d  # directory
ls -latr
tree
tree -d  # directory only
ls -R  # recursive
file file
du -k file  # size in K
du -m file  # size in M
du -h file  # human readable
du -c dir  # total

touch file
mkdir dir
mkdir -p a/b/c  # parent directory
rmdir dir
rmdir -p a/b/c  # parent directory
rm file
rm -r dir  # recursive
rm -f file  # force
cp src dest
cp src1 src2 dest_dir
cp -r src_dir dest_dir  # recursive
mv scr dest
tar -cf file.tar dir  # create
tar -tf file.tar  # display
tar -xf file.tar  # extract
tar -zcf file.tgz dir  # zip
tar -ztf file.tgz
ln -s file link

find  ## all files 
find dir 
find file_name/pattern  # current dir
find -name file_name/pattern  # recursive find
find -iname File_name/pattern  # ignore case
find -not -name pattern
find -ls  # list
find -mtime +1 -mtime -3  # modified time in days
find -size +1M -size -5M  # size
find -type d  # directory
find -type f  # file
find -newer file  # newer
find -exec cmd {} \;  # execute cmd
find -exec file {} \;

cmd >file
cmd >>file
cmd 2>/dev/null
cmd 2>&1
cmd >file 2>&1

cut -d: -f1,2-3,4-  # delimiter, fields
cut -d' ' -f2
sort
sort -k2  # key is column 2
sort -r  # reverse
sort -u  # unique
tr ',' ' '
tr -s ' ' '\n'  # squeze space
uniq -c - count
awk '{print $1, $2}'
column -t
grep pattern file | cut -d, -f1,3 | sort | tr "," " " | column -t
ps |grep hugo  | awk '{print $1'} | xargs kill

cat file
cat -n file  # line number
tac file
less -N file  # line number
head -5 file  # lines
tail -5 file  # lines
tail -f file  # follow update

grep pattern file
grep -i pattern file  # ignore case
grep -n pattern file  # line number
grep -c pattern file  # count
grep -v  pattern file  # not match
cmd | grep pattern
strings binary | grep pattern
grep pattern file | less

diff file1 file2
sdiff file1 file2
vimdiff file1 file2

ps -f  # details
ps -e  # every proces
ps -ef
ps -u user  # user's
ps -H  # tree
pstree
top
cmd&
Ctrl+z  # suspend
Ctrl+c  # kill
jobs -l
bg %1
fg %1
kill pid
kill %jobid
kill -9 pid

whoami
su username
useradd username -c "User" -m -s /bin/bash -g default_group
useradd svcname -c "Service" -r -d /bin/svc -s /bin/false
useradd svcname -c "Service" -u uid -d /bin/svc -s /bin/false
usermod username -aG g1,g2
userdel username
passwd username
groupadd groupname -c "Group" -g gid
groupdel groupname
groupmod groupname
groups
groups username
id
id username
tail -1 /etc/passwd
tail -1 /etc/group

chgrp group file
chmod 660 file
chmod u+rwx,g-w,o= file  # user, group, other
chmod a+r file  # all
umask
umask 0002