Linux and networking

chmod : The chmod command allows you to alter access rights to files and directories. the shell prompt type: ls -alt You should see some files with the following in front of them example: drwxrwsr-x 7 rajesh 1024 Apr 6 14:30 drwxr-s--x 22 rajini 1024 Mar 30 18:20 d-wx-wx-wx 3 Cheguevara1024 Apr 6 14:30 What do the letters mean in front of the files/directories mean? r indicates that it is readable w indicates that it is writable x indicates that it is executable - indicates that no permission to manipulate has been assigned When listing your files, the first character lets you know whether you’re looking at a file or a directory. It’s not part of the security settings. The next three characters indicate Your access restrictions. The next three indicate your group's permissions, and finally other users' permissions. chmod 755 filename The example above will grant you full rights, group rights to execute and read, and all others access to execute the file. 7 permission Fu...

Permissions For security reasons, all Unix systems including Linux have file permissions which allow you to control access to directories - who can read, write, or execute a file or command in a directory. In the extreme left is either a d or hyphen (-) indicating whether this is a directory or a file (occasionally you will also see an l indicating a link). Then you see three groups of the same three letters in the same order: r for read, w for write, x for execute, and the hyphen (-) for no permission given in that type. The first group of three letters is for the owner, the second group for the group, and the third the world. Whoever creates the file is the owner, and if more than one person is working on a project or needs access to this file they are given permission as a group, and finally how the file is open to anyone who has access to the system (the world). chmod, chown, chgrp The command to change file permissions is chmod (change mode). There are two ways for do...

command cd : Use cd change directories example: cd home or complete path must be written cd /root/home command clear : clean up your command window command ls : The ls command lists the contents of your current working directory command mkdir : makes directory command df : df provides a very quick check of your file system disk space. command du : du display usage of the disk space example du -a command finger : finger allows you to see who else is on the system or get detailed information about a person who has access to the system. command man : man followed by a command will give detailed information about that command Example: man ls command logout : logout will log your account out of the system command find : find will locate a files/directories qui...

/etc : This directory contains most of the basic Linux system-configuration Files /etc/sysconfig : Contains important system configuration files that are created and maintained by various services (including iptables, samba, and most networking services) /etc/sysconfig/network : Network configuration file used by the system during the boot process. /etc/sysconfig/network-scripts : Configuration files that are run during boot process related to setting up of your network. /etc/xinetd.d : Contains a set of files, each of which defines a network service that the xinetd daemon listens for on a particular port. /etc/resolv.conf : Host name resolver configuration file. This configures Linux so that it ...

Command w : Shows who is currently logged in system Command who : shows who is on logged in on the server in an shell Command netstat : Shows all current network connections Command netstat -apn : Shows all connections to the server, the source and destination ips and ports Command netstat -rn : Shows routing table for all ips bound to the server Command top : Shows live system processes in a formatted table, memory information, uptime and other useful info While in top, Shift + M to sort by memory usage or Shift + P to sort by CPU usage Command top -u root : Show processes running by user root only Command route -n : Shows routing table for all ips bound to the server Command nslookup yahoo.com : Query your default domain name server (DNS) for an Internet name (or IP number) host_to_find Command traceroute yahoo.com : Have a look how you messages travel to yahoo.com Command tracepath yahoo.com : Performs a very similar function ...

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