Summary #4 - Network & System Administration (NSA)

Linux Filesystem Management

badblocks -search disk or partition for badblocks. (badblocks device) (badblocks hda)
df - Shows disk free space on one or more filesystems. (df –k, df -h)
du - Shows how much disk space a directory and all its files contain. (du , du –sk , du –sh )
fsck - Filesystem check. Must not be run on a mounted file system. (fsck )
sync - Synchronize data on disk with memory. `sync' writes any data buffered in memory out to disk.
mount - mount a filesystem.  (mount , mount –a)
umount - Unmounts a filesystem. (umount )

Network Management Command

dnsdomainname -Show systems DNS domain name
hostname -show/set the name of your machine for networking
nisdomainname -Show/set systems NIS/YP domain name
ypdomainname - Show/set the system's NIS/YP domain name
arp -let the user read or modify their arp cache.
dig - Send domain name query packets to name servers for debugging or testing.
finger - Display information about the system users. Ex: finger Deepak
ftp -File transfer program. (ftp
ifconfig -Configure a network interface.
e.g: ifconfig eth0 address 172.31.2.2 netmask 255.255.0.0
ifdown - Shutdown network interface.
e.g: ifdown eth0
ifup -Brings a network interface up.
e.g: ifup eth0
netconf -GUI interactive program,let you configure a network on Redhat systems.
netconfig -GUI step by step network configuration program.
netstat - Displays information about the systems network connections,
(port connections, routing tables, and more)
"netstat -r" ->display the routing table. (netstat –rn)
nslookup - query DNS servers for information about hosts.
ping -Send ICMP ECHO_REQUEST packets to network hosts. (ping
route -Show or manipulate the IP routing table. (route, route add, route del)
showmount -Show mount information for an NFS server.
ssh -Secure Login (ssh )
tcpdump -Dump network traffic,Prints headers of packets that match the boolean expression. (tcpdump eth0)
telnet -User interface to the TELNET protocol, setting up a remote console session. (telnet )
traceroute -Print the route that packets take to the specified network host. (traceroute )

Communications commands (includes mail)
 
elm -Electronic mail.
pine -Program for internet news and e-mail, Can send documents, graphics, local & remote messages.
talk -Lets two parties talk simultaneously.
mail --send mail

System Management Command

Runtime level management
exit -Terminates the shell.
halt -Stop the system.
init -Process control initialization. (init 3)
logout -Log the user off the system.
poweroff -Brings the system down.
reboot -Reboot the system
runlevel -List the current and previous runlevel

shutdown
If system has many users, use the command shutdown -h +time ‘`,
time-time in minutes until the system is halted
message-short explanation of why the system is shutting down.
e.g:: # shutdown -h +10 'We will install a new disk. System should be back on-line in three hours.‘

passwd -Set user's password. (passwd, passwd )
quota -Display users' limits and current disk usage. (quota, quota )
quotaoff -Turns filesystem quotas off.
quotaon -Turns filesystem quotas on.
quotacheck -check filesystem for usage, and update the quota.user file.
edquota -edit user/group quotas. (edquota )

su -Single user login. (su -)
useradd -Create new user/update default new user information. (useradd –g -s -c –d
userdel -Delete user account & related files. (userdel )
usermod -Modify a user account.
users -Print the user names of users currently logged in.
wall -Send message to everybody's terminal. (wall “text message”)
who -Display the users logged in.
whoami -Print effective user id.

System Time
cal -Calendar. (cal, cal 2005)
date -Print/set the system date and time. (date, date MMDDhhmm[[CC]YY][.ss])
hwclock -Set/read the hardware CMOS clock.
uptime -Reports how long the system has been running.

Linux Job & Process Management

Linux Process Management
ps -Get -status of one/more processes.
PPID-parent process ID ;  
PID-process ID
Eg: ps ax |more to see all processes including daemons
Eg : ps –ef | grep
pstree -Display the tree of running processes.
pgrep -looks through the currently running processes and lists
the  process IDs which matches the selection criteria to stdout.
All the criteria have to match.

top  ->dynamic real-time view of a running system.
display system summary information,list  of  tasks currently  being managed by the Linux kernel