File Management Creation
mktemp
Creates a temporary file with a random name. Guarantees that the new file doesn’t exist
touch new_file.txt new_file_2.txt
Creates both new_file.txt and new_file_2.txt
touch file_name_{a..c}
Creates file_name_a, file_name_b,
and file_name_c
Moving
cp file_name.txt file_name_copy.txt
Creates a copy of file_name.txt named
file_name_copy.txt in the same working directory
Reading
head file_name.txt
Prints first 10 lines of a file
tail file_name.txt
Prints last 10 lines of a file
touch new_file.txt
Creates a new file
touch {new_file, new_file_2}.txt
Creates both new_file.txt and new_file_2.txt
touch file_name_{1..3}
Creates file_name_1, file_name_2,
and file_name_3
`mv file_name.txt new_file_copy.txt`
Moves file_name.txt to new_file_copy.txt in the same directory, renaming the file
cat file_name.txt
Prints full contents of a file
less file_name.txt
Prints a part of file contents
Deletion
rm file_name.txt
Removes a file
wc file_name.txt
Prints number of lines words and characters in the file
rm -f file_name.txt
Removes a file ignoring non-existent files
Compression and Decompression
zip archive_name.zip file_name_1.php file_name_2.php
tar -cvf archive_name.tar file_name_1.php file_name_2.php
tar -zcf archive_name.tar.gz file_name_1.php file_name_2.php
Archives separate files (depending on the format)
zip -r archive_name.zip directory
tar -cvf archive_name.tar directory
tar -zcf archive_name.tar.gz directory
Archives a whole directory (depending on the format)
Replacing in Files
unzip archive_name.zip
tar -xvf archive_name.tar
tar -zxvf archive_name.tar.gz
Extracts an archive (depending on the format)
sed -i 's/search_query/replace_query/' file_name.txt
Modifies the content of the original file if the replacement query exists in the file
sed 's/search_query/replace_query/g' `file_name.txt` > `new_file_name.txt`
Replaces search_query with replace_query in file_name.txt and saves everything in new_file_name.txt
sed 's/search_query/replace_query/g' file_name.txt
Replaces search_query with replace_query in file_name.txt
Search in Files
grep 'contents' /file_name.txt
Searches for contents inside file_name.txt
grep 'contents_1|contents_2' /directory -R
Searches for contents or contents_2
inside directory recursively
grep 'contents' /directory -i
Performs case-insensitive search
grep 'contents' /directory -x
Matches the entire line and prints it out
grep 'contents' /directory -l
Only displays files that match contents query
Directories Navigation
cd directory
Goes to the listed sub-directory
cd -
Goes to the previous directory
ls -l
Shows where symbolic links are pointing
grep 'contents' /directory -r
Searches for contents inside directory recursively
grep 'contents' /directory -v
Displays only the lines that don’t match contents
grep 'contents' /directory -i
Performs case-insensitive search
grep 'contents' /directory -n
Displays line numbers along with the results
grep 'contents' /directory -L
Only shows files that don’t match contents query
cd
Goes to the home directory
ls
Lists all directories
ls -l -h
Lists all directories in long format, -h flag uses the human-readable format
cd ..
Goes the directory one level up from the current directory
ls -a
Lists all directories, including hidden ones
ls -t
List directories by modification time, showing newest first
cd ~
tree
Shows directory and file trees
stat `file.txt`
Lists file’s size alongside created and modified timestamps
Creation
mkdir new_directory
Creates a new directory
mkdir -p parent/child/nested_child
Creates nested directories
mktemp -d
Creates a temporary directory with a random name. Guarantees that the new directory doesn’t exist
Moving
mv old_directory new_directory Moves old_directory to new_directory
cp -r directory directory_copy
Copies directory to directory_copy recursively
tree -d
Shows directory tree tree -a Shows directory and file trees, including hidden ones
stat directory
Lists directory’s size alongside created and modified timestamps
pwd
Shows current directory path
mkdir new_directory_1 directory_2
Creates multiple new directories
mkdir -p {dir_one, dir_two}/nested
Creates multiple nested directories
cp directory directory_copy Copies directory to directory_copy
Deletion
rmdir directory
Removes directory
rm -r directory
Removes dicrectory recursively
Symbolic Links
ln -s path link
Creates a symbolic link called link to the path directory
ln -s -f path link
Overwrites existing symbolic link called link
Popular Directory Permission
777
All possible permissions. Not recommended for security reasons.
755
Directory owner has full permissions. Other users can list the directory but won’t be able to manage the files.
700
Directory owner has full permissions. Other users have no permissions.
Permission Management
ls -l
Displays directory contents in a long format, which displays both permissions and ownership
chown :new_group file_name
Changes group for file_name
chmod u=rwx, g=r, o-rwx file_name
Sets file_name read, write, execute permissions for the owner and other users, leaving read-only permissions for the group
chmod u+x file_name.txt
Sets the user permissions to execute
chmod u+x, g+x, o+x file_name.txt
chmod a+x file_name.txt
chmod +x file_name.txt
Sets everyone's permissions to execute
chown username:new_group file_name Changes both the owner and group
for file_name
chown username file_name
Changes the owner for file_name
chmod 777 -R directory
Sets read, write and execute permissions for everyone in directory recursively
chmod g+x file_name.txt
Sets the group permissions to execute
Arrays Creation
indexed_array = (element_1, element_2, element_3)
Creates an index array
declare -A associative_array = ([key_1] = element_1, [key_2] = element_2, [key_3] = element_3)
Creates an associative array
Adding Elements
indexed_array += (new_element)
Adds a new element to an indexed array
Printing Out
echo ${indexed_array[0]}
Prints out the first array element
associative_array += ([key_1] = new_element
Adds a new element to an associative array (note that the key needs to be provided as well)
echo ${indexed_array[@]}
Prints out the whole array
echo ${!associative_array[@]}
Prints out all the keys for an associative array
Deletion
unset indexed_array[2]
Removes the third element from an indexed array
unset associative_array[key]
Removes the key element from an associative array
Resource Usage and Processes
top htop
Lists out all the processes interactively
nice -n 10 process_name
Changes the priority to
10 for process_name
kill 2468
Kills a process that has process ID 2468
jobs -p
Shows all processes jobs alongside their IDs
du
Shows current directory, sub-directories and file sizes
Shutdown and Reboot
ps all
Lists out all currently running processes
renice 10 2468
Changes the priority to 10 for a
process that has process ID 2468
killall process_name
Kills all processes that have process_name in their name
lsof
Shows all open files and processes that use them
du /directory/sub-directory
Lists specified directory, sub-directories and file sizes
pidof process_name
Prints out the process ID of process_name
ps -o ni 2468
Displays the priority for a process ID 2468
jobs
Shows all background processes
free
Displays memory usage
df
Shows disks alongside their used and available space
shutdown -r
reboot
Immediately reboots the system
shutdown
Shuts the system down after one minute
shutdown -r +10
Reboots the system after 10 minutes
shutdown now
Immediately shuts down the system
shutdown -c
Cancels a shutdown or reboot
shutdown +10
Shuts the system down after 10 minutes
reboot -f
Forces a reboot
Scheduled Tasks Crontab Syntax
Access via crontab -e
[minute] [hour] [day] [month] [week] [command]
Each line represents one command to be run as directed
crontab -i
Will show a prompt before removing a user’s crontab
@daily cat /home/hello_world.sh
Schedules a background job to run every day
@reboot cat /home/hello_world.sh
Schedules a job to run after each system reboot
crontab -l
Used to view crontab entries (cron jobs), and display system crontab file contents
crontab -r
Will remove the current crontab file
* * * * * cat /home/hello_world.sh
Schedules a job to run every minute
00 08-17 * * * cat /home/hello_world.sh
Schedules a job to run every weekday, including weekends, from 8am to 5pm
@monthly cat /home/hello_world.sh
Schedules a job to run at the beginning of each month
0 12,15,17,19,21 * * * cat /home/hello_world.sh
Schedules a job to be run five times a day at 12pm, 3pm, 5pm, 7pm and, 9pm
HTTP Requests
curl https://domain.tld
Returns response body for domain.tld
curl -o file.txt https://domain.tld Outputs to a text file
Network and DNS
ip addr
Shows all IP addresses on a system
ping -c 15 -i 3 domain.tld
Pings the domain 10 times, 3 seconds apart
traceroute domain.tld
Displays all servers the network traffic goes through
curl -i https://domain.tld
Returns response body for domain.tld and includes status code and HTTP headers
curl -H|--header "User-Agent: Agent" https://domain.tld
Adds an HTTP header
ip route show
Shows all IP addresses to router
netstat -l
Shows all open ports
nmap 0.0.0.0
Scans for the 1,000 most commonly open ports on localhost
host example.net
Display IPv4 and IPv6 addresses for domain.tld
ping domain.tld
Sends multiple ICMP protocol ping requests netstat -i Shows all open ports with in/out usage
nmap 255.255.255.255
Scans for the 1,000 most commonly open ports on remote IP address
dig example.net
Display complete DNS information
dig example.net +short
Display complete DNS in short format
dig example.net ns
Query NS records
dig example.net txt
Query TXT records dig example.net A Query A records
dig example.net cname
Query CNAME records
dig example.net MX Query MX records
Secure Shell Protocol (SSH)
ssh hostname
Connects to hostname using current username via default SSH port 22
ssh root@255.255.255.255 -p 1023
Connects via given username and IP via given SSH port
ssh root@255.255.255.255
Connects via given username and IP via default SSH port 22
