Check the version of kernel running
The command free displays information about RAM and swap space usage, showing the total and the used amount in both categories.
top provides a quick overview of the currently running processes. Press H to access a page that briefly explains the main options to customize the program.
diff [option(s)] file1 file2
The diff command compares the contents of any two files. The output produced by the program lists all lines that do not match.
This is frequently used by programmers who need only send their program alterations and not the entire source code.
du [option(s)] [path]
This command, when executed without any parameters, shows the total disk space occupied by files and subdirectories in the current directory.
Default umask Value
The user file-creation mode mask (umask) is use to determine the file permission for newly created files. It can be used to control the default file permission for new files. It is a four-digit octal number.
List of Well-Known Ports
Port numbers range from 0 to 65536, but only port numbers 0 to 1024 are reserved for privileged services and designated as well-known ports. This list of well-known port numbers specifies the port used by the server process as its contact port.
|1||TCP Port Service Multiplexer (TCPMUX)|
|5||Remote Job Entry (RJE)|
|18||Message Send Protocol (MSP)|
|20||FTP — Data|
|21||FTP — Control|
|22||SSH Remote Login Protocol|
|25||Simple Mail Transfer Protocol (SMTP)|
|42||Host Name Server (Nameserv)|
|49||Login Host Protocol (Login)|
|53||Domain Name System (DNS)|
|69||Trivial File Transfer Protocol (TFTP)|
|108||SNA Gateway Access Server|
|115||Simple File Transfer Protocol (SFTP)|
|137||NetBIOS Name Service|
|139||NetBIOS Datagram Service|
|143||Interim Mail Access Protocol (IMAP)|
|150||NetBIOS Session Service|
|179||Border Gateway Protocol (BGP)|
|190||Gateway Access Control Protocol (GACP)|
|194||Internet Relay Chat (IRC)|
|197||Directory Location Service (DLS)|
|389||Lightweight Directory Access Protocol (LDAP)|
|396||Novell Netware over IP|
|444||Simple Network Paging Protocol (SNPP)|