PAM is an authentication layer that allows programs to be written independent of specific authentication scheme.The application request authentication via the PAM library  and PAM library determines whether the user is allowed to proceed.If an administrator wants to implement a different authentication,he just change the PAM configuration files and existing program work seamlessly. All application [...]

Top is an invaluable tool for actively monitoring the processes running on linux system.With top you are able to view the most CPU intensive tasks,manipulate processes or track the system perfomance over time. Top updates its output every 5 seconds bydefault.The output consists of a header block of information showing overall system statistics,and a process [...]

RPC portmapper is a server that converts RPC program number into a TCP/IP or UDP/IP protocol port numbers.It must be running in order to make RPC calls to RPC servers on that machine.When an RPC server is started,it will tell portmap what port number it is listening to and what RPC program number it is [...]

All unix files have its description stored in a structure called inode that is identified by an inode number .The inode contain information about file size,time of last access,time of last modification ,permission etc The i node value contains the following fields 1).File owner identifier 2).File type 3).File access permissions 4).File access times 5).Number of [...]

The ntsysv utility provides a simple interface for activating or deactivating services.ntsysv used to tern  an xinted managed service on or off. It can also used to configure runlevels.By default,only the current runlevel is configured.To configure a different runlevel you can use ntsysv utility. eg: #ntsysv –level 345

chattr enables you to set special attributes on files.You can set files to repress updating the access time,or set files to be append only, immutable or undeletable.You can also use ‘chattr’ to ensure secure deletion of a file.Only root user can use this command.chattr command works only on ext2 and ext3  filesystems. The structure of [...]

sysctl is an interface that allows you to make changes to a running linux kernel.With /etc/sysctl.conf,you can configure various linux networking and system setting such as limit network transmited configuration for ipv4 & ipv6 Turn on exe sheild protection prevent against the common flood attack Turn on source IP address verification prevent a cracker from [...]

vmstat command report statistics about kernel thread,virtual memory,disks,traps and CPU activity.Reports generated by vmstat command can be used to balance system load activity.These system-wide statistics are calculated as average for values expressed as percentages and sum otherwise. If the vmstat command is invoked without flags,the report contains a summary of the virtual memory activity since [...]

iostat (input/output statistics) is a system monitor tool used to collect and show operating system storage input and output statistics.The iostat command generates various utilization and throughput reports according to the options specified with iostat.Report generated by the iostat command consists of system configuration information and various utilization and throughput reports.iostat command generates two types [...]

scp command is to copy files and directories securely between remote hosts without logging into the remote systems explicitly.scp command uses ssh to transfer data between hosts.So it requires password for authentication.scp encrypts both files and password exchanged to perform secure transfer. The general syntax for scp command is scp [options] [[user@]host1:]filename1 … [[user@]host2:]filename2 eg: [...]