CheatSheet
Display Linux system information
uname -a
Display kernel release information
uname -r
Show how long the system has been running + load
uptime
Show system host name
hostname
Display the IP addresses of the host
hostname -I
Show system reboot history
last reboot
Show the current date and time
date
Show this month’s calendar
cal
Display who is online
w
Who you are logged in as
whoami
Display messages in kernel ring buffer
dmesg
Display CPU information
cat /proc/cpuinfo
Display memory information
cat /proc/meminfo
Display free and used memory ( -h for human readable, -m for MB, -g for GB.)
free -h
Display PCI devices
lspci -tv
Display USB devices
lsusb -tv
Display DMI/SMBIOS (hardware info) from the BIOS
dmidecode
Show info about disk sda
hdparm -i /dev/sda
Perform a read speed test on disk sda
hdparm -tT /dev/sda
Test for unreadable blocks on disk sda
badblocks -s /dev/sda
Display and manage the top processes
top
Interactive process viewer (top alternative)
htop
Display processor related statistics
mpstat 1
Display virtual memory statistics
vmstat 1
Display I/O statistics
iostat 1
Display the last 100 syslog messages (Use /var/log/syslog for Debian based systems.)
tail 100 /var/log/messages
Capture and display all packets on interface eth0
tcpdump -i eth0
Monitor all traffic on port 80 ( HTTP )
tcpdump -i eth0 'port 80'
List all open files on the system
lsof
List files opened by user
lsof -u user
Display free and used memory ( -h for human readable, -m for MB, -g for GB.)
free -h
Execute “df -h”, showing periodic updates
watch df -h
Display the user and group ids of your current user.
id
Display the last users who have logged onto the system.
last
Show who is logged into the system.
who
Show who is logged in and what they are doing.
w
Create a group named “test”.
groupadd test
Create an account named john, with a comment of “John Smith” and create the user’s home directory.
useradd -c "John Smith" -m john
Delete the john account.
userdel john
Add the john account to the sales group
usermod -aG sales john
List all files in a long listing (detailed) format
ls -al
Display the present working directory
pwd
Create a directory
mkdir directory
Remove (delete) file
rm file
Remove the directory and its contents recursively
rm -r directory
Force removal of file without prompting for confirmation
rm -f file
Forcefully remove directory recursively
rm -rf directory
Copy file1 to file2
cp file1 file2
Copy source_directory recursively to destination. If destination exists, copy source_directory into destination, otherwise create destination with the contents of source_directory.
cp -r source_directory destination
Rename or move file1 to file2. If file2 is an existing directory, move file1 into directory file2
mv file1 file2
Create symbolic link to linkname
ln -s /path/to/file linkname
Create an empty file or update the access and modification times of file.
touch file
View the contents of file
cat file
Browse through a text file
less file
Display the first 10 lines of file
head file
Display the last 10 lines of file
tail file
Display the last 10 lines of file and “follow” the file as it grows.
tail -f file
Display your currently running processes
ps
Display all the currently running processes on the system.
ps -ef
Display process information for processname
ps -ef | grep processname
Display and manage the top processes
top
Interactive process viewer (top alternative)
htop
Kill process with process ID of pid
kill pid
Kill all processes named processname
killall processname
Start program in the background
program &
Display stopped or background jobs
bg
Brings the most recent background job to foreground
fg
Brings job n to the foreground
fg n
Linux chmod example
PERMISSION EXAMPLE
U G W
rwx rwx rwx chmod 777 filename
rwx rwx r-x chmod 775 filename
rwx r-x r-x chmod 755 filename
rw- rw- r-- chmod 664 filename
rw- r-- r-- chmod 644 filename
NOTE: Use 777 sparingly!
LEGEND
U = User
G = Group
W = World
r = Read
w = write
x = execute
- = no access
Display all network interfaces and ip address
ifconfig -a
Display eth0 address and details
ifconfig eth0
Query or control network driver and hardware settings
ethtool eth0
Send ICMP echo request to host
ping host
Display whois information for domain
whois domain
Display DNS information for domain
dig domain
Reverse lookup of IP_ADDRESS
dig -x IP_ADDRESS
Display DNS ip address for domain
host domain
Display the network address of the host name.
hostname -i
Display all local ip addresses
hostname -I