Display free and used memory ( -h for human readable, -m for MB, -g for GB.)
lspci -tv
Display PCI devices
lsusb -tv
Display USB devices
dmidecode
Display DMI/SMBIOS (hardware info) from the BIOS
hdparm -i /dev/sda
Show info about disk sda
hdparm -tT /dev/sda
Perform a read speed test on disk sda
badblocks -s /dev/sda
Test for unreadable blocks on disk sda
3 - PERFORMANCE MONITORING AND STATISTICS
Command
Notes
top
Display and manage the top processes
htop
Interactive process viewer (top alternative)
mpstat 1
Display processor related statistics
vmstat 1
Display virtual memory statistics
iostat 1
Display I/O statistics
tail 100 /var/log/messages
Display the last 100 syslog messages (Use /var/log/syslog for Debian based systems.)
tcpdump -i eth0
Capture and display all packets on interface eth0
tcpdump -i eth0 ‘port 80’
Monitor all traffic on port 80 ( HTTP )
lsof
List all open files on the system
lsof -u user
List files opened by user
free -h
Display free and used memory
( -h for human readable, -m for MB, -g for GB.)
watch df -h
Execute “df -h”, showing periodic updates
4 - USER INFORMATION AND MANAGEMENT
Command
Notes
id
Display the user and group ids of your current user.
last
Display the last users who have logged onto the system.
who
Show who is logged into the system.
w
Show who is logged in and what they are doing.
groupadd test
Create a group named “test”.
useradd -c “John Smith” -m john
Create an account named john, with a comment of “John Smith” and create the user’s home directory.
userdel john
Delete the john account.
usermod -aG sales john
Add the john account to the sales group
5 - FILE AND DIRECTORY COMMANDS
Command
Notes
ls -al
List all files in a long listing (detailed) format
pwd
Display the present working directory
mkdir directory
Create a directory
rm file
Remove (delete) file
rm -r directory
Remove the directory and its contents recursively
rm -f file
Force removal of file without prompting for confirmation
rm -rf directory
Forcefully remove directory recursively
cp file1 file2
Copy file1 to file2
cp -r source_directory destination
Copy source_directory recursively to destination. If destination exists, copy source_directory into destination, otherwise create destination with the contents of source_directory.
mv file1 file2
Rename or move file1 to file2. If file2 is an existing directory, move file1 into directory file2
ln -s /path/to/file linkname
Create symbolic link to linkname
touch file
Create an empty file or update the access and modification times of file.
cat file
View the contents of file
less file
Browse through a text file
head file
Display the first 10 lines of file
tail file
Display the last 10 lines of file
tail -f file
Display the last 10 lines of file and “follow” the file as it grows.
6 - PROCESS MANAGEMENT
Command
Notes
ps
Display your currently running processes
ps -ef
Display all the currently running processes on the system.
ps -ef
grep processname
top
Display and manage the top processes
htop
Interactive process viewer (top alternative)
kill pid
Kill process with process ID of pid
killall processname
Kill all processes named processname
program &
Start program in the background
bg
Display stopped or background jobs
fg
Brings the most recent background job to foreground
fg n
Brings job n to the foreground
7 -FILE PERMISSIONS
PERMISSION
EXAMPLE
U – G – W
rwx rwx rwx
chmod 777 filename # Use sparingly!
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
LEGEND
U = User r = Read
G = Group w = write
W = World x = execute
- = no access
8 - NETWORKING
Command
Notes
ifconfig -a
Display all network interfaces and ip address
ifconfig eth0
Display eth0 address and details
ethtool eth0
Query or control network driver and hardware settings