Linux Cheat Sheets commands#
This contains different heloers for commands on a linux os.
Unix Command-Line Utilities Cheat-Sheet#
Using Cron and placing crontab files#
CRON Fields#
| Field | Allowed Values | Description |
|---|---|---|
MINUTE | 0-59 | Trigger every MINUTE minute(s) |
HOUR | 0-23 | Trigger every HOUR hour(s) |
DAY OF MONTH | 1-31 | Trigger on specific DAY of the month |
MONTH | 1-12 | Trigger in MONTH month(s) |
DAY OF WEEK | 0-6 (Sun-Sat) | Trigger on specific DAY OF WEEK, where Sunday = 0 |
Special Characters in CRON#
| Special Character | Description |
|---|---|
* | Represents all possible values for the field |
, | Separates items in a list |
- | Specifies a range of values |
/ | Specifies increments |
CRON Expression Examples#
| Cron Expression | Description |
|---|---|
* * * * * | Executes every minute |
0 * * * * | Executes on the hour every hour |
0 0 * * * | Executes at midnight every day |
0 0 1 * * | Executes at midnight on the first of every month |
30 20 * * 6 | Executes at 8:30 PM every Saturday |
*/5 * * * * | Executes every five minutes |
0 0 8-10 * * * | Executes on the hour every hour from 8 AM to 10 AM |
Executing a Script and Redirecting Output to a Log File#
0 5 * * * /path/to/script.sh >> /path/to/logfile.log 2>&1
This CRON job example runs a script located at /path/to/script.sh every day at 5 AM, appending both standard output and standard error to /path/to/logfile.log.
Common CRON Directories and Files#
| Location/File | Description |
|---|---|
/etc/crontab | System-wide crontab file where administrators can define CRON jobs. |
/etc/cron.d | Directory for additional system-wide cron job files. CRON jobs in this directory allow for easier management of individual cron job configurations. |
/etc/cron.daily | Directory for scripts that need to run daily. |
/etc/cron.hourly | Directory for scripts that need to run hourly. |
/etc/cron.weekly | Directory for scripts that need to run weekly. |
/etc/cron.monthly | Directory for scripts that need to run monthly. |
/var/spool/cron/crontabs | Directory where individual user crontab files are stored. Users can schedule their personal jobs using the crontab command. |
/etc/cron.allow | File containing usernames that are allowed to use crontab. If this file exists, only users listed in it can schedule cron jobs. |
/etc/cron.deny | File containing usernames that are denied access to crontab. If cron.allow does not exist, all users except those listed in cron.deny can schedule jobs. |
Example of Adding a System-Wide CRON Job#
To add a system-wide CRON job, you might place a file in /etc/cron.d/. Here’s an example of what the contents might look like:
# Example CRON job in /etc/cron.d/myjob
0 5 * * * root /usr/local/bin/daily-task.sh
MySQL Cheat-Sheet#
Connect to MySQL#
| Command | Description |
|---|---|
mysql -u root -p | Connect to MySQL as root user |
mysql -u <user> -p | Connect to MySQL as a specific user |
mysql -u root -p -h <host> | Connect to MySQL on a specific host |
Backup and Restore#
| Command | Description |
|---|---|
mysqldump -u root -p <database> > backup.sql | Backup a database to a file |
mysql -u root -p <database> < backup.sql | Restore a database from a file |
PostgreSQL Cheat-Sheet#
Connect to PostgreSQL#
| Command | Description |
|---|---|
psql -U postgres | Connect to PostgreSQL as the postgres user |
psql -U <user> -d <database> | Connect to PostgreSQL as a specific user and database |
psql -U <user> -d <database> -h <host> | Connect to PostgreSQL on a specific host |
PostreSQL CLI Commands#
| Command | Description |
|---|---|
\c <database> | Connect to a specific database |
\password <user> | Change password for a specific user |
\l | List all databases |
\d+ | Show detailed information about various database objects |
\dt | List all tables in the current database |
\du | List all users |
\df | List all functions |
\dv | List all views |
\dn | List all schemas |
\dp | List all permissions |
\di | List all indexes |
\ds | List all sequences |
\d+ | Show detailed information about various database objects |
\q | Quit psql |
\x | Toggle expanded output |
Backup and Restore#
| Command | Description |
|---|---|
pg_dump <database> > backup.sql | Backup a database to a file |
psql <database> < backup.sql | Restore a database from a file |
Patterns#
Grep Cheat-Sheet#
| Command | Description |
|---|---|
grep 'pattern' file | Search for a pattern in a file |
grep -i 'pattern' file | Case insensitive search |
grep -r 'pattern' dir | Recursively search for a pattern in all files under the directory |
grep -v 'pattern' file | Invert match to display lines that do not contain the pattern |
grep -n 'pattern' file | Display the line numbers with the output |
grep -c 'pattern' file | Count the number of lines that match the pattern |
grep -l 'pattern' * | Show only the names of files with matching lines |
grep -L 'pattern' * | Show only the names of files without matching lines |
grep -o 'pattern' file | Show only the part of a line matching the pattern |
grep 'pattern1|pattern2' file | Search for lines matching pattern1 or pattern2 |
grep -A 3 'pattern' file | Display 3 lines after the matching line |
grep -B 3 'pattern' file | Display 3 lines before the matching line |
grep -C 3 'pattern' file | Display 3 lines before and after the matching line |
grep '^pattern' file | Match lines beginning with ‘pattern’ |
grep 'pattern$' file | Match lines ending with ‘pattern’ |
grep '^[^#]' file | Ignore lines starting with ‘#’ (comments) |
| `grep -E ‘patt(ern1 | ern2)’ file` |
grep -w 'pattern' file | Match whole word ‘pattern’ |
grep -f patterns.txt file | Use patterns from the file, one per line |
grep -e 'pattern1' -e 'pattern2' file | Search for multiple patterns |
SED Cheat-Sheet#
| Command | Description |
|---|---|
sed 's/pattern/replacement/' file | Replace the first occurrence of a pattern in each line |
sed -i 's/pattern/replacement/' file | Replace all occurrences of a pattern in the file (in-place editing) |
sed '/pattern/d' file | Delete lines that match the pattern |
sed '2d' file | Delete the second line of the file |
sed '2,$d' file | Delete from the second line to the end of the file |
sed 's/pattern/replacement/g' file | Replace all occurrences of a pattern in each line |
sed -n 'p' file | Print the output (useful with -n to suppress other output) |
sed '/pattern/p' file | Print only lines that match the pattern |
sed '1,5s/pattern/replacement/' file | Apply the substitution to lines 1 to 5 only |
sed -e 'command1' -e 'command2' file | Apply multiple editing commands in sequence |
sed '5q' file | Print until the 5th line of the file then quit |
sed 's/[a-z]/\U&/g' file | Convert lowercase letters to uppercase |
SORT Cheat-Sheet#
| Command | Description |
|---|---|
sort file | Sort lines of text alphabetically in a file |
sort -n file | Sort numerically (useful for sorting numbers) |
sort -r file | Reverse the results of sorts (descending order) |
sort -o output_file file | Write the result to the output_file instead of standard output |
sort -k 2 file | Sort a file based on the second column of data |
sort -u file | Sort and remove duplicate lines |
sort -t':' -k 3n file | Sort a file using ‘:’ as a delimiter and numerically by the third column |
sort -f file | Ignore case while sorting |
sort -m file1 file2 | Merge already sorted files file1 and file2 |
sort -c file | Check whether the file is already sorted; do not sort |
AWK Cheat-Sheet#
| Command | Description |
|---|---|
awk '/pattern/ {print $1}' | standard Unix shells |
awk '/pattern/ {print "$1"}' | compiled with DJGPP, Cygwin |
awk "/pattern/ {print \"$1\"}" | GnuWin32, UnxUtils, Mingw |
awk '1;{print ""}' | double space a file |
awk 'BEGIN{ORS="\n\n"};1' | double space a file |
awk 'NF{print $0 "\n"}' | double space a file which already has blank lines |
awk '1;{print "\n"}' | triple space a file |
awk '{print FNR "\t" $0}' files* | precede each line by its line number |
awk '{print NR "\t" $0}' files* | precede each line by its line number for all files together |
awk '{printf("%5d : %s\n", NR,$0)}' | number each line of a file |
awk 'NF{$0=++a " :" $0};1' | number each line of a file, but only print numbers if line is not blank |
awk 'END{print NR}' | count lines (emulates “wc -l”) |
awk '{s=0; for (i=1; i<=NF; i++) s=s+$i; print s}' | print the sums of the fields of every line |
awk '{for (i=1; i<=NF; i++) s=s+$i}; END{print s}' | add all fields in all lines and print the sum |
awk '{for (i=1; i<=NF; i++) if ($i < 0) $i = -$i; print }' | print every line after replacing each field with its absolute value |
awk '{for (i=1; i<=NF; i++) $i = ($i < 0) ? -$i : $i; print }' | print every line after replacing each field with its absolute value |
awk '{ total = total + NF }; END {print total}' file | print the total number of fields (“words”) in all lines |
awk '/Beth/{n++}; END {print n+0}' file | print the total number of lines that contain “Beth” |
awk '$1 > max {max=$1; maxline=$0}; END{ print max, maxline}' | print the largest first field and the line that contains it |
awk '{ print NF ":" $0 }' | print the number of fields in each line, followed by the line |
awk '{ print $NF }' | print the last field of each line |
awk '{ field = $NF }; END{ print field }' | print the last field of the last line |
awk 'NF > 4' | print every line with more than 4 fields |
awk '$NF > 4' | print every line where the value of the last field is > 4 |
Network#
Ethtool Cheat-Sheet#
Displaying Information#
| Command | Description |
|---|---|
ethtool <interface> | Display information about a specific network interface |
ethtool -i <interface> | Display driver information |
ethtool -a <interface> | Display all settings |
ethtool -k <interface> | Display offload settings |
ethtool -c <interface> | Display coalescing settings |
ethtool -g <interface> | Display ring buffer settings |
ethtool -l <interface> | Display large receive offload settings |
ethtool -S <interface> | Display statistics |
ethtool -t <interface> | Test the network interface for offloading capabilities |
ethtool -T <interface> | Display time stamping settings |
ethtool -x <interface> | Display channel settings |
ethtool -P <interface> | Display permanent MAC address |
ethtool -N <interface> | Display offload settings |
ethtool -u <interface> | Display bus information |
ethtool -d <interface> | Display register dump |
ethtool -g <interface> | Display ring buffer settings |
Setting Parameters#
| Command | Description |
|---|---|
ethtool -G <interface> | Set ring buffer settings |
ethtool -L <interface> | Set large receive offload settings |
ethtool -A <interface> | Set pause parameters |
ethtool -C <interface> | Set coalescing settings |
ethtool -K <interface> | Set offload settings |
ethtool -N <interface> | Set offload settings |
ethtool -p <interface> | Blink the LED on the network interface |
ethtool -r <interface> | Reset the network interface |
ARP in Linux#
| Command | Description |
|---|---|
arp | View the ARP table |
arp -a | View the ARP table |
arp -n | View the ARP table (don’t resolve names) |
arp -d <ip> | Delete an entry from the ARP table |
arp -s <ip> <mac_address> | Add an entry to the ARP table |
arp -i <interface> -s <ip> <mac_address> | Add an entry to the ARP table for a specific interface |
arp -i <interface> -d <ip> | Delete an entry from the ARP table for a specific interface |
arp -i <interface> -n | View the ARP table for a specific interface |
arp -i <interface> -a | View the ARP table for a specific interface |
ip neigh show | View the ARP table |
ip neigh show <ip> | View the ARP table for a specific IP address |
ip neigh add <ip> lladdr <mac_address> dev <interface> | Add an entry to the ARP table |
ip neigh change <ip> lladdr <mac_address> dev <interface> | Change an entry in the ARP table |
ip neigh del <ip> dev <interface> | Delete an entry from the ARP table |
ip neigh flush dev <interface> | Flush the ARP table for a specific interface |
ip neigh flush all | Flush the ARP table |
ip -s neigh show | Show ARP statistics |
ip -s neigh flush all | Flush the ARP cache |
Linux One-Liners#
This table provides useful one-liner commands for Linux users, ideal for system administration and development tasks.
| Command | Description |
|---|---|
ps auxf | sort -nr -k 3 | head -10 | Display a tree of system processes, sorted by memory usage. |
df -h | Check available disk space on all mounted filesystems in a human-readable format. |
top | Monitor real-time system processes. |
lsof -p $$ | List all open files by a specific process (replace $$ with the process ID). |
wc -l filename | Count the number of lines in a file named filename. |
sort -n -t . -k 1,1 -k 2,2 -k 3,3 -k 4,4 file | Sort a list of IP addresses stored in a file. |
sort file | uniq -c | sort -nr | head | Find the most frequently occurring lines in a file, useful for log analysis. |
netstat -tuln | Check all listening ports on the system. |
wget --mirror -p --convert-links -P ./LOCAL-DIR website-url | Download a website and all of its assets for offline viewing, storing in LOCAL-DIR. |
tar czf backup.tar.gz /path/to/directory | Create a compressed backup of a directory. |
newuser="xyzuser" && sudo useradd -m $newuser && echo "$newuser ALL=(ALL) NOPASSWD: ALL" | sudo tee /etc/sudoers.d/$newuser | Create a new user defined by newuser, and add a sudoers file for them with NOPASSWD enabled. |
ls -lhtr --color=always | Sort by last writen to reverse |
