find all files changed three days ago

find . -ctime -3

find . -ctime +0 -a -ctime -3

to create an empty file use the editor

vi /path/filename

remove a file:

rm /path/filename

remove a whole directory:

rm -r /path/filename

copy a file

cp /pathfrom/filename /pathto/filename

move or rename a file or directory

mv /pathfrom/filename /pathto/filename

change directory

cd /path

go back one directory

cd ..

create a user:

useradd -d /usr/share/nginx/html -s /usr/sbin/nologin USERNAME

check if a group exists:

grep GROUPNAME /etc/group

create a group:

groupadd GROUPNAME

add a user to a group:

usermod -a -G GROUPNAME USERNAME

check user groups:

id USERNAME

make a directory

mkdir /path/directory

change file or directory permissions

chmod 755 filepath

chmod u+rw-x filepath

give permissions to user for /path/file

chown user:group /path/file

give permissions to /path/directory for all files in that directory

chown -R user /path/directory

view content of a file

cat path/filename

find a string in a file:

open to the directory you want to search:

cd /path

then type:

grep -r -i STRING_TO_SEARCH_FOR ./

what's the path of the folder, i'm into right now, type:

pwd

CENTOS COMMANDS

cent os list installed packages

rpm -qa | less

then press "q" to quit

reboot server

reboot

find the version of installed kernel

uname -r

make sure a program gets started when server (re-)boots

chkconfig --add mysqld

or with set levels

chkconfig --levels 235 mysqld on

check runlevels

chkconfig --list

find a file

locate filename

find a file in a folder

locate filename | grep /foldername

updatedb

check which software is listening to ports

nmap -v -sT localhost