Essentials
#Linux
General
whoami
Find out what user we're currently logged in as.
man man
Shows info about man command and lists all the sections of the manual.
strace objFile
Lists all the system calls used in the program.
ltrace objFile
Lists all the library calls used in the program.
gcc -o objFile source -v
Lists all the path of libraries and headers used in creation of objFile
Network commands
-u
Lists all the active UDP connections showing domain names.
-n
Lists all the active, showing IP and port numbers.
nslookup domain
Shows the IP address related to the domain (E.g. IP of www.google.it)
dig @server name type
DNS lookup utility:
server name or IP address of the name server to query;
name name of the resource record that is to be looked up;
type type of query is required (ANY, A, MX, SIG, etc.). If no type is specified, A is performed by default.
wc [file]
Prints in order newlines, words, and bytes (characters) counts for file. If file not specified or equal to -, counts from stdin.
route
-n
Show numerical addresses instead of trying to determine symbolic hostnames in routing table.
arp
-a
List all the MAC addresses stored after some ARP requests and replies made by our ethernet interfaces.
ifconfig
List network interfaces.
Directories and files
ls
-a
List all files, including hidden ones (filename starting with ".")
-color
Colored list [=always/never/auto]
-l
List with long format (show permissions)
-h
List with readable file size
-r
List in reverse order
-R
List recursively directory tree
-s
List file size
-S
Sort by file size
-t
Sort by time & date
-X
Sort by extension name
Search patterns in strings
grep
STRING file
Search STRING in file
-e pattern
Specify pattern
-i
Case insensitive
-v
Invert match (List all string without matches)
-c
Output count of matching lines only
-l
Output matching files only
-n
Precede each matching line with a line number
-b
A historical curiosity: precede each matching line with a block number
-h
Output matching lines without preceding them by file names
-s
Suppress error messages about nonexistent or unreadable files
-w
Force PATTERN to match only whole words
-x
Force PATTERN to match only whole lines
-f file
Take regexes from a file
-o
Output the matched parts of a matching line
Manage files and dir
cd
Take regexes from a file
cp X PATH
Make a copy of file/folder X into the path PATH
mv X PATH
Move/rename the file/folder X in PATH
cat X
Concatenate file content of X
pwd
Print working directory
touch FILE
Create a file with name FILE
rm FILE
Delete a file with name FILE
mkdir DIR
Create a directory with name DIR
rmdir DIR
Delete an empty directory with name DIR
rm -r DIR
Delete recursively a directory with name DIR
Switch between users
su
USERNAME
Switch to USERNAME user by staying in the current folder
-l USERNAME
Switch to USERNAME user by switching to USERNAME home folder
--login USERNAME
Switch to USERNAME user by switching to USERNAME home folder
Process management
&
If specified at the end of the command, run it in background.
&&
Combine multiple commands together in one line of your terminal.
;
Execute several command in order (one after the other).
Process status
ps
-f
See background processes
-e
More info about processes
-a
Select all processes except both session leaders and processes not associated with a terminal/td>
-u USERLIST
Select by effective user ID (EUID) or name
fg PID
It continues the stopped job with id PID by running it in the foreground
bg
A job control command that resumes suspended jobs (CTRL+Z)
kill PID
It kills the job with id PID
top
It shows all the processes running in Linux working environment
htop
It shows all the processes running in Linux working environment
UNIX common Files
/etc/services
List all the applications with their port/td>
/etc/protocols
Internet protocols.
/usr/include/x86\_64-linux-gnu/bits/socket.h
List all the protocol type possible for socket.
/usr/include/x86\_64-linux-gnu/sys/socket.h
Definition of struct sockaddr and specific ones.
Shell operators
!!
Previous launched command
<
Redirection of the command input (overwriting text)
>
Redirection of the command output (overwriting text)
>>
Redirection of the of the command output (appending text)
Download files
Command
Description
wget URL
Download to the current folder
wget -O <new_filename> URL
Download with a different name
wget -c URL
Resume download
curl -O URL
Download to the current folder
curl -o <new_filename> URL
Download with a different name
curl -C - -O URL
Resume download
SCP
SFTP
SMB
Then, inside the prompt:
Transfer files
Transfer a file from the SOURCE path to the DEST path, using SSH channel:
SOURCE and DEST have the following format:
or
Automation
Open the crontab by running the following command:
A crontab is simply a special file with formatting that is recognised by the cron process to execute each line step-by-step.\ The crontab will execute each line as a cronjob.\
Crontab line fomat
Each line of the crontab has the following format:
HOUR
What hour to execute at
DOM
What day of the month to execute at
MON
What month of the year to execute at
DOW
What day of the week to execute at
cmd
The actual command that will be executed
Special time interval statements
@annually
@daily
Run the cronjob every day at 12:00am
@midnight
@monthly
Run the job once a month, on the 1st, at 12:00am
@weekly
Run the job once a week at 12:00am on Sunday
@hourly
Run the job at the top of every hour
@reboot
Run the task once, at startup
Open crontab with different user
Time management
Current time
Available timezone
Set new timezone
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