PoiNtEr->: May 2011

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Saturday, May 28, 2011

Safe Reboot Of Linux Using Magic SysRq Key

The magic SysRq key is a key combination in the Linux kernel which allows the user to perform various low level commands regardless of the system’s state.

It is often used to recover from freezes, or to reboot a computer without corrupting the filesystem. The key combination consists of Alt+SysRq+commandkey. In many systems the SysRq key is the printscreen key.
First, you need to enable the SysRq key, as shown below.
echo "1" > /proc/sys/kernel/sysrq

List of SysRq Command Keys

Following are the command keys available for Alt+SysRq+commandkey.
  • ‘k’ – Kills all the process running on the current virtual console.
  • ’s’ – This will attempt to sync all the mounted file system.
  • ‘b’ - Immediately reboot the system, without unmounting partitions or syncing.
  • ‘e’ – Sends SIGTERM to all process except init.
  • ‘m’ – Output current memory information to the console.
  • ‘i’ - Send the SIGKILL signal to all processes except init
  • ‘r’ - Switch the keyboard from raw mode (the mode used by programs such as X11), to XLATE mode.
  • ’s’ – sync all mounted file system.
  • ‘t’ - Output a list of current tasks and their information to the console.
  • ‘u’ - Remount all mounted filesystems in readonly mode.
  • ‘o’ – Shutdown the system immediately.
  • ‘p’ – Print the current registers and flags to the console.
  • ‘0-9' - Sets the console log level, controlling which kernel messages will be printed to your console.
  • ‘f’ - Will call oom_kill to kill process which takes more memory.
  • ‘h’ – Used to display the help. But any other keys than the above listed will print help.
We can also do this by echoing the keys to the /proc/sysrq-trigger file. For example, to re-boot a system you can perform the following.
echo "b" > /proc/sysrq-trigger

Perform a Safe reboot of Linux using Magic SysRq Key

To perform a safe reboot of a Linux computer which hangs up, do the following. This will avoid the fsck during the next re-booting. i.e Press Alt+SysRq+letter highlighted below.
  • unRaw (take control of keyboard back from X11,
  • tErminate (send SIGTERM to all processes, allowing them to terminate gracefully),
  • kIll (send SIGILL to all processes, forcing them to terminate immediately),
  • Sync (flush data to disk),
  • Unmount (remount all filesystems read-only),
  • reBoot.

Thursday, May 26, 2011

how to change MAC Address in ubuntu

Open up a terminal and switch to root user.
Suppose : xx:xx:xx:xx:xx:xx = new mac address you wan to assign to you box
example: 1a:2b:3c:4d:5e:6f
Characters allowed in mac address: 1 2 3 4 5 6 7 8 9 0 a b c d e f
enter the following:
# ifconfig eth0 down
# ifconfig eth0 hw ether 1a:2b:3c:4d:5e:6f
# ifconfig etho up
Check the new MAC address by using following command
# ifconfig

Hacking Tools For Ubuntu


Nmap is one of the best network security scanners out there. Nmap will scan for all the computers and services that are currently running on the network. This application will not only scan for the available services on the network like most other port scanners do, Nmap will try to gather as much information as it can about the remote computers such as which operating system they are using, device type, firewall information, current uptime & the vendor of the network card in use.


Nmap is included within Ubuntu's repositories. So to install, use the following command:
sudo apt-get install nmap

NetCat is a fantastic little program written by a guy called 'Hobbit' in 1991. This tool is used for reading and writing to network locations using connections on either UDP or TCP.
Again, NetCat is also in the repositories, so to install, run the following command:
sudo apt-get install netcat


Aircrack-ng is the best tool out there for cracking and recovering 802.11 WEP & WPA-PSK keys. Once you have collected enough data packets, you are then able to recover the key from the data packets. This is defiantly a must have application to test your home wireless security

To install:
sudo apt-get install aircrack-ng

Ettercap: it for seeing user-name and there passwords... example if someone logins into yahoo, you would have the username and password.

Driftnet: create a folder and activate driftnet. driftnet will add images to the folder so you can view them, like if someone was to go to an adult site you would know it!

dsniff: which it has urlsnarf. urlsnarf will let you see the urls of the people on your network goes to.

How to Install and Configure DHCP Server in Ubuntu Server

A DHCP Server assigns IP address to client computers. This is very often used in enterprise networks to reduce configuration efforts. All IP addresses of  all computers are stored in a database that resides on a server machine.
A DHCP server can provide configuration settings using two methods
Address Pool
This method entails defining a pool (sometimes also called a range or scope) of IP addresses from which DHCP clients are supplied their configuration properties dynamically and on a fist come first serve basis. When a DHCP client is no longer on the network for a specified period, the configuration is expired and released back to the address pool for use by other DHCP Clients.
MAC Address
This method entails using DHCP to identify the unique hardware address of each network card connected to the network and then continually supplying a  constant configuration each time the DHCP client makes a request to the DHCP server using that network device.

Install DHCP server in ubuntu
sudo apt-get install dhcp3-server
This will complete the installation.
Configuring DHCP server
If you have two network cards in your ubuntu server you need to select which interface you want to use for  DHCP server listening.By default it listens to eth0.
You can change this by editing  /etc/default/dhcp3-server file
sudo vi /etc/default/dhcp3-server
Find this line
Replace with the following line
Save and exit.This is optional.
Next you need to make a backup copy of /etc/dhcp3/dhcpd.conf file
cp /etc/dhcp3/dhcpd.conf /etc/dhcp3/dhcpd.conf.back
Edit /etc/dhcp3/dhcpd.conf file using the following command
sudo vi /etc/dhcp3/dhcpd.conf
Using address pool method
You need to change the following sections in /etc/dhcp3/dhcpd.conf file
default-lease-time 600;
max-lease-time 7200;
option subnet-mask;
option broadcast-address;
option routers;
option domain-name-servers,;
option domain-name “yourdomainname.com”;
subnet netmask {
save and exit the file
This will result in the DHCP server giving a client an IP address from the range . It will lease an IP address for 600 seconds if the client doesn’t ask for a specific time frame. Otherwise the maximum (allowed) lease will be 7200 seconds. The server will also “advise” the client that it should use as its subnet mask, as its broadcast address, as the router/gateway and and as its DNS servers.
Using MAC address method
This method is you can reserver some of the machines or all the machines with fixed ip address.In the following example i am using fixed ip address for server1,server2,printer1 and printer2
default-lease-time 600;
max-lease-time 7200;
option subnet-mask;
option broadcast-address;
option routers;
option domain-name-servers,;
option domain-name “yourdomainname.com”;
subnet netmask {
host server1 {
hardware ethernet 00:1b:63:ef:db:54;
host server2 {
hardware ethernet 00:0a:95:b4:d4:b0;
host printer1 {
hardware ethernet 00:16:cb:aa:2a:cd;
host printer2 {
hardware ethernet 00:0a:95:f5:8f:b3;
Now you need to restart dhcp server using the following command
sudo /etc/init.d/dhcp3-server restart
Configure Ubuntu DHCP Client
If you want to configure your ubuntu desktop as DHCP client following this procedure
You need to open /etc/network/interfaces file
sudo vi /etc/network/interfaces
make sure you have the following lines (eth0 is an example)
auto lo eth0
iface eth0 inet dhcp
iface lo inet loopback
Save and exit the file
You need to restart networking services using the following command
sudo /etc/init.d/networking restart
How to find DHCP server IP address
You need to use the following commands
sudo dhclient
tail -n 15 /var/lib/dhcp3/dhclient.*.leases

Wednesday, May 25, 2011

Setting up local dns cache and public dns address

When it comes to internet, reasonable speed is always an most important  thing that no one ready to compromise with. That may be a crucial reason for making you sit infront of your machines for hours and days. So the lightning speed can be achieved with your ubuntu box in two ways. They are 
  • Use faster and free domain name servers like google's pubic dns or OpenDNS (first throw the one provided by your service provider). .

  • Maintain a local dns cache in your machine itself.  So that you can do a good amount of address resolution for frequently used websites within your machine itself, and that saves a reasonable amount of time.

Here i am planning to bring both of these techniques together in a simple manner. Though there are many applications for local DNS caching in ubuntu [ such as dnsmasq, pdnsd, bind9 ] are available, bind9 seems to be a good option for me...

Starting with BIND9  DNS server in Ubuntu

Bind9 (Berkly Internet Naming Daemon)  is the most widely deployed DNS server. Bind9 is available in the ubuntu main repository itself. So you don't need to add some additional repository for installing it. Use the following command line or search for 'bind9' in Synaptic package manager to install it. 

$ sudo apt-get install bind9

Bind9 allows different type of configurations, and our point of view is on configuring it as a caching server. In this configuration BIND9 will find the answer to name queries and remember the answer for the next query. This can be useful for a slow internet connections especially based on mobile internet. By caching DNS queries, you will reduce bandwidth and (more importantly) latency. It increase network performance by caching IP addresses of commonly visited websites instead of retrieving them from the public DNS servers maintained by ISPs at each request.

Configuring the BIND server 

#  First you have to set your machine's address ( itself as the primary dns address.  This can be done with the help of Network manager or by editing the /etc/resolv.conf file in your ubuntu box. Check the screenshot below..

  • using Network manager:: select the connection and click on the edit. Then choose the IPv4 settings tab and add to the DNS servers field.

  • editing the resolv.conf file:: If you are using DHCP then you may have to edit the resolv.conf file every time you connect to the internet to make bind work properly.

Now change the bind configuration file to add some external DNS servers for resolving a new address that is not cached on your local cache at that time. If you are not adding an external dns server, then it will not be possible to resolve a new address request comes from the browser.  Here i recommend google's public dns( or OpenDNS addresses to add in the BIND configuration file. This servers may be sometimes faster and reliable than your ISP's Domain Name Servers. You can find the best DNS server applicable for you by googling. Here is how i have added it

#  First open the file 'named.conf.options

$ sudo gedit /etc/bind/named.conf.options

#  Now uncommend the section 'forwarders'. Replace the '' with the dns server address applicable to you (Check the figure).



#  Restart  the BIND server:

$ sudo /etc/init.d/bind9 restart


Thatz it. We are almost done. Now use the dig command to see the change in speed. If you "dig" a domain name multiple times you should see a drastic decrease in query time: between the first and second query. This is due to the server caching the query. See what happened when i dig twitter from my terminal three times concecutively. See the change in the Query time.

$ dig twitter.com


;; Query time: 0 msec
;; WHEN: Thu May 26 01:50:14 2011
;; MSG SIZE  rcvd: 295


Friday, May 20, 2011

Linux System Monitoring Tools Every SysAdmin Should Know

Need to monitor Linux server performance? Try these built-in command and a few add-on tools. Most Linux distributions are equipped with tons of monitoring. These tools provide metrics which can be used to get information about system activities. You can use these tools to find the possible causes of a performance problem. The commands discussed below are some of the most basic commands when it comes to system analysis and debugging server issues such as:
  1. Finding out bottlenecks.
  2. Disk (storage) bottlenecks.
  3. CPU and memory bottlenecks.
  4. Network bottlenecks.

#1: top - Process Activity Command

The top program provides a dynamic real-time view of a running system i.e. actual process activity. By default, it displays the most CPU-intensive tasks running on the server and updates the list every five seconds.
Fig.01: Linux top command
Fig.01: Linux top command

Commonly Used Hot Keys

The top command provides several useful hot keys:
Hot Key Usage
t Displays summary information off and on.
m Displays memory information off and on.
A Sorts the display by top consumers of various system resources. Useful for quick identification of performance-hungry tasks on a system.
f Enters an interactive configuration screen for top. Helpful for setting up top for a specific task.
o Enables you to interactively select the ordering within top.
r Issues renice command.
k Issues kill command.
z Turn on or off color/mono

#2: vmstat - System Activity, Hardware and System Information

The command vmstat reports information about processes, memory, paging, block IO, traps, and cpu activity.
# vmstat 3
Sample Outputs:
procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
 0  0      0 2540988 522188 5130400    0    0     2    32    4    2  4  1 96  0  0
 1  0      0 2540988 522188 5130400    0    0     0   720 1199  665  1  0 99  0  0
 0  0      0 2540956 522188 5130400    0    0     0     0 1151 1569  4  1 95  0  0
 0  0      0 2540956 522188 5130500    0    0     0     6 1117  439  1  0 99  0  0
 0  0      0 2540940 522188 5130512    0    0     0   536 1189  932  1  0 98  0  0
 0  0      0 2538444 522188 5130588    0    0     0     0 1187 1417  4  1 96  0  0
 0  0      0 2490060 522188 5130640    0    0     0    18 1253 1123  5  1 94  0  0

Display Memory Utilization Slabinfo

# vmstat -m

Get Information About Active / Inactive Memory Pages

# vmstat -a

#3: w - Find Out Who Is Logged on And What They Are Doing

w command displays information about the users currently on the machine, and their processes.
# w username
# w vivek

Sample Outputs:
17:58:47 up 5 days, 20:28,  2 users,  load average: 0.36, 0.26, 0.24
USER     TTY      FROM              LOGIN@   IDLE   JCPU   PCPU WHAT
root     pts/0       14:55    5.00s  0.04s  0.02s vim /etc/resolv.conf
root     pts/1       17:43    0.00s  0.03s  0.00s w

#4: uptime - Tell How Long The System Has Been Running

The uptime command can be used to see how long the server has been running. The current time, how long the system has been running, how many users are currently logged on, and the system load averages for the past 1, 5, and 15 minutes.
# uptime
18:02:41 up 41 days, 23:42,  1 user,  load average: 0.00, 0.00, 0.00
1 can be considered as optimal load value. The load can change from system to system. For a single CPU system 1 - 3 and SMP systems 6-10 load value might be acceptable.

#5: ps - Displays The Processes

ps command will report a snapshot of the current processes. To select all processes use the -A or -e option:
# ps -A
Sample Outputs:
    1 ?        00:00:02 init
    2 ?        00:00:02 migration/0
    3 ?        00:00:01 ksoftirqd/0
    4 ?        00:00:00 watchdog/0
    5 ?        00:00:00 migration/1
    6 ?        00:00:15 ksoftirqd/1
 4881 ?        00:53:28 java
 4885 tty1     00:00:00 mingetty
 4886 tty2     00:00:00 mingetty
 4887 tty3     00:00:00 mingetty
 4888 tty4     00:00:00 mingetty
 4891 tty5     00:00:00 mingetty
 4892 tty6     00:00:00 mingetty
 4893 ttyS1    00:00:00 agetty
12853 ?        00:00:00 cifsoplockd
12854 ?        00:00:00 cifsdnotifyd
14231 ?        00:10:34 lighttpd
14232 ?        00:00:00 php-cgi
54981 pts/0    00:00:00 vim
55465 ?        00:00:00 php-cgi
55546 ?        00:00:00 bind9-snmp-stat
55704 pts/1    00:00:00 ps
ps is just like top but provides more information.

Show Long Format Output

# ps -Al
To turn on extra full mode (it will show command line arguments passed to process):
# ps -AlF

To See Threads ( LWP and NLWP)

# ps -AlFH

To See Threads After Processes

# ps -AlLm

Print All Process On The Server

# ps ax
# ps axu

Print A Process Tree

# ps -ejH
# ps axjf
# pstree

Print Security Information

# ps -eo euser,ruser,suser,fuser,f,comm,label
# ps axZ
# ps -eM

See Every Process Running As User Vivek

# ps -U vivek -u vivek u

Set Output In a User-Defined Format

# ps -eo pid,tid,class,rtprio,ni,pri,psr,pcpu,stat,wchan:14,comm
# ps axo stat,euid,ruid,tty,tpgid,sess,pgrp,ppid,pid,pcpu,comm
# ps -eopid,tt,user,fname,tmout,f,wchan

Display Only The Process IDs of Lighttpd

# ps -C lighttpd -o pid=
# pgrep lighttpd
# pgrep -u vivek php-cgi

Display The Name of PID 55977

# ps -p 55977 -o comm=

Find Out The Top 10 Memory Consuming Process

# ps -auxf | sort -nr -k 4 | head -10

Find Out top 10 CPU Consuming Process

# ps -auxf | sort -nr -k 3 | head -10

#6: free - Memory Usage

The command free displays the total amount of free and used physical and swap memory in the system, as well as the buffers used by the kernel.
# free
Sample Output:
total       used       free     shared    buffers     cached
Mem:      12302896    9739664    2563232          0     523124    5154740
-/+ buffers/cache:    4061800    8241096
Swap:      1052248          0    1052248

#7: iostat - Average CPU Load, Disk Activity

The command iostat report Central Processing Unit (CPU) statistics and input/output statistics for devices, partitions and network filesystems (NFS).
# iostat
Sample Outputs:
Linux 2.6.18-128.1.14.el5 (www03.nixcraft.in)  06/26/2009

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           3.50    0.09    0.51    0.03    0.00   95.86

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda              22.04        31.88       512.03   16193351  260102868
sda1              0.00         0.00         0.00       2166        180
sda2             22.04        31.87       512.03   16189010  260102688
sda3              0.00         0.00         0.00       1615          0

#8: sar - Collect and Report System Activity

The sar command is used to collect, report, and save system activity information. To see network counter, enter:
# sar -n DEV | more
To display the network counters from the 24th:
# sar -n DEV -f /var/log/sa/sa24 | more
You can also display real time usage using sar:
# sar 4 5
Sample Outputs:
Linux 2.6.18-128.1.14.el5 (www03.nixcraft.in)   06/26/2009

06:45:12 PM       CPU     %user     %nice   %system   %iowait    %steal     %idle
06:45:16 PM       all      2.00      0.00      0.22      0.00      0.00     97.78
06:45:20 PM       all      2.07      0.00      0.38      0.03      0.00     97.52
06:45:24 PM       all      0.94      0.00      0.28      0.00      0.00     98.78
06:45:28 PM       all      1.56      0.00      0.22      0.00      0.00     98.22
06:45:32 PM       all      3.53      0.00      0.25      0.03      0.00     96.19
Average:          all      2.02      0.00      0.27      0.01      0.00     97.70

#9: mpstat - Multiprocessor Usage

The mpstat command displays activities for each available processor, processor 0 being the first one. mpstat -P ALL to display average CPU utilization per processor:
# mpstat -P ALL
Sample Output:
Linux 2.6.18-128.1.14.el5 (www03.nixcraft.in)   06/26/2009

06:48:11 PM  CPU   %user   %nice    %sys %iowait    %irq   %soft  %steal   %idle    intr/s
06:48:11 PM  all    3.50    0.09    0.34    0.03    0.01    0.17    0.00   95.86   1218.04
06:48:11 PM    0    3.44    0.08    0.31    0.02    0.00    0.12    0.00   96.04   1000.31
06:48:11 PM    1    3.10    0.08    0.32    0.09    0.02    0.11    0.00   96.28     34.93
06:48:11 PM    2    4.16    0.11    0.36    0.02    0.00    0.11    0.00   95.25      0.00
06:48:11 PM    3    3.77    0.11    0.38    0.03    0.01    0.24    0.00   95.46     44.80
06:48:11 PM    4    2.96    0.07    0.29    0.04    0.02    0.10    0.00   96.52     25.91
06:48:11 PM    5    3.26    0.08    0.28    0.03    0.01    0.10    0.00   96.23     14.98
06:48:11 PM    6    4.00    0.10    0.34    0.01    0.00    0.13    0.00   95.42      3.75
06:48:11 PM    7    3.30    0.11    0.39    0.03    0.01    0.46    0.00   95.69     76.89

#10: pmap - Process Memory Usage

The command pmap report memory map of a process. Use this command to find out causes of memory bottlenecks.
# pmap -d PID
To display process memory information for pid # 47394, enter:
# pmap -d 47394
Sample Outputs:
47394:   /usr/bin/php-cgi
Address           Kbytes Mode  Offset           Device    Mapping
0000000000400000    2584 r-x-- 0000000000000000 008:00002 php-cgi
0000000000886000     140 rw--- 0000000000286000 008:00002 php-cgi
00000000008a9000      52 rw--- 00000000008a9000 000:00000   [ anon ]
0000000000aa8000      76 rw--- 00000000002a8000 008:00002 php-cgi
000000000f678000    1980 rw--- 000000000f678000 000:00000   [ anon ]
000000314a600000     112 r-x-- 0000000000000000 008:00002 ld-2.5.so
000000314a81b000       4 r---- 000000000001b000 008:00002 ld-2.5.so
000000314a81c000       4 rw--- 000000000001c000 008:00002 ld-2.5.so
000000314aa00000    1328 r-x-- 0000000000000000 008:00002 libc-2.5.so
000000314ab4c000    2048 ----- 000000000014c000 008:00002 libc-2.5.so
00002af8d48fd000       4 rw--- 0000000000006000 008:00002 xsl.so
00002af8d490c000      40 r-x-- 0000000000000000 008:00002 libnss_files-2.5.so
00002af8d4916000    2044 ----- 000000000000a000 008:00002 libnss_files-2.5.so
00002af8d4b15000       4 r---- 0000000000009000 008:00002 libnss_files-2.5.so
00002af8d4b16000       4 rw--- 000000000000a000 008:00002 libnss_files-2.5.so
00002af8d4b17000  768000 rw-s- 0000000000000000 000:00009 zero (deleted)
00007fffc95fe000      84 rw--- 00007ffffffea000 000:00000   [ stack ]
ffffffffff600000    8192 ----- 0000000000000000 000:00000   [ anon ]
mapped: 933712K    writeable/private: 4304K    shared: 768000K
The last line is very important:
  • mapped: 933712K total amount of memory mapped to files
  • writeable/private: 4304K the amount of private address space
  • shared: 768000K the amount of address space this process is sharing with others

#11 and #12: netstat and ss - Network Statistics

The command netstat displays network connections, routing tables, interface statistics, masquerade connections, and multicast memberships. ss command is used to dump socket statistics. It allows showing information similar to netstat. See the following resources about ss and netstat commands:

#13: iptraf - Real-time Network Statistics

The iptraf command is interactive colorful IP LAN monitor. It is an ncurses-based IP LAN monitor that generates various network statistics including TCP info, UDP counts, ICMP and OSPF information, Ethernet load info, node stats, IP checksum errors, and others. It can provide the following info in easy to read format:
  • Network traffic statistics by TCP connection
  • IP traffic statistics by network interface
  • Network traffic statistics by protocol
  • Network traffic statistics by TCP/UDP port and by packet size
  • Network traffic statistics by Layer2 address
Fig.02: General interface statistics: IP traffic statistics by network interface
Fig.02: General interface statistics: IP traffic statistics by network interface
Fig.03 Network traffic statistics by TCP connection
Fig.03 Network traffic statistics by TCP connection

#14: tcpdump - Detailed Network Traffic Analysis

The tcpdump is simple command that dump traffic on a network. However, you need good understanding of TCP/IP protocol to utilize this tool. For.e.g to display traffic info about DNS, enter:
# tcpdump -i eth1 'udp port 53'
To display all IPv4 HTTP packets to and from port 80, i.e. print only packets that contain data, not, for example, SYN and FIN packets and ACK-only packets, enter:
# tcpdump 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)'
To display all FTP session to, enter:
# tcpdump -i eth1 'dst and (port 21 or 20'
To display all HTTP session to
# tcpdump -ni eth0 'dst and tcp and port http'
Use wireshark to view detailed information about files, enter:
# tcpdump -n -i eth1 -s 0 -w output.txt src or dst port 80

#15: strace - System Calls

Trace system calls and signals. This is useful for debugging webserver and other server problems. See how to use to trace the process and see What it is doing.

#16: /Proc file system - Various Kernel Statistics

/proc file system provides detailed information about various hardware devices and other Linux kernel information. See Linux kernel /proc documentations for further details. Common /proc examples:
# cat /proc/cpuinfo
# cat /proc/meminfo
# cat /proc/zoneinfo
# cat /proc/mounts

17#: Nagios - Server And Network Monitoring

Nagios is a popular open source computer system and network monitoring application software. You can easily monitor all your hosts, network equipment and services. It can send alert when things go wrong and again when they get better. FAN is "Fully Automated Nagios". FAN goals are to provide a Nagios installation including most tools provided by the Nagios Community. FAN provides a CDRom image in the standard ISO format, making it easy to easilly install a Nagios server. Added to this, a wide bunch of tools are including to the distribution, in order to improve the user experience around Nagios.

18#: Cacti - Web-based Monitoring Tool

Cacti is a complete network graphing solution designed to harness the power of RRDTool's data storage and graphing functionality. Cacti provides a fast poller, advanced graph templating, multiple data acquisition methods, and user management features out of the box. All of this is wrapped in an intuitive, easy to use interface that makes sense for LAN-sized installations up to complex networks with hundreds of devices. It can provide data about network, CPU, memory, logged in users, Apache, DNS servers and much more. See how to install and configure Cacti network graphing tool under CentOS / RHEL.

#19: KDE System Guard - Real-time Systems Reporting and Graphing

KSysguard is a network enabled task and system monitor application for KDE desktop. This tool can be run over ssh session. It provides lots of features such as a client/server architecture that enables monitoring of local and remote hosts. The graphical front end uses so-called sensors to retrieve the information it displays. A sensor can return simple values or more complex information like tables. For each type of information, one or more displays are provided. Displays are organized in worksheets that can be saved and loaded independently from each other. So, KSysguard is not only a simple task manager but also a very powerful tool to control large server farms.
Fig.05 KDE System Guard
Fig.05 KDE System Guard {Image credit: Wikipedia}
See the KSysguard handbook for detailed usage.

#20: Gnome System Monitor - Real-time Systems Reporting and Graphing

The System Monitor application enables you to display basic system information and monitor system processes, usage of system resources, and file systems. You can also use System Monitor to modify the behavior of your system. Although not as powerful as the KDE System Guard, it provides the basic information which may be useful for new users:
  • Displays various basic information about the computer's hardware and software.
  • Linux Kernel version
  • GNOME version
  • Hardware
  • Installed memory
  • Processors and speeds
  • System Status
  • Currently available disk space
  • Processes
  • Memory and swap space
  • Network usage
  • File Systems
  • Lists all mounted filesystems along with basic information about each.
Fig.06 The Gnome System Monitor application
Fig.06 The Gnome System Monitor application

Bonus: Additional Tools

A few more tools:
  • nmap - scan your server for open ports.
  • lsof - list open files, network connections and much more.
  • ntop web based tool - ntop is the best tool to see network usage in a way similar to what top command does for processes i.e. it is network traffic monitoring software. You can see network status, protocol wise distribution of traffic for UDP, TCP, DNS, HTTP and other protocols.
  • Conky - Another good monitoring tool for the X Window System. It is highly configurable and is able to monitor many system variables including the status of the CPU, memory, swap space, disk storage, temperatures, processes, network interfaces, battery power, system messages, e-mail inboxes etc.
  • GKrellM - It can be used to monitor the status of CPUs, main memory, hard disks, network interfaces, local and remote mailboxes, and many other things.
  • vnstat - vnStat is a console-based network traffic monitor. It keeps a log of hourly, daily and monthly network traffic for the selected interface(s).
  • htop - htop is an enhanced version of top, the interactive process viewer, which can display the list of processes in a tree form.
  • mtr - mtr combines the functionality of the traceroute and ping programs in a single network diagnostic tool.

Howto: Linux Add User To Group

How can I add a user to a group under Linux operating system?

You can use the useradd or usermod commands to add a user to a group. The useradd command creates a new user or update default new user information. The usermod command modifies a user account i.e. it is useful to add user to existing group. There are two types of group. First is primary user group and other is secondary group. All user account related information is stored in /etc/passwd, /etc/shadow and /etc/group files to store user information.

useradd Example - Add A New User To Secondary Group

You need to the useradd command to add new users to existing group (or create a new group and then add user). If group does not exist, create it. The syntax is as follows:
useradd -G {group-name} username
In this example, create a new user called vivek and add it to group called developers. First login as a root user (make sure group developers exists), enter:
# grep developers /etc/group
If you do not see any output then you need to add group developers using groupadd command:
# groupadd developers
Next, add a user called vivek to group developers:
# useradd -G developers vivek
Setup password for user vivek:
# passwd vivek
Ensure that user added properly to group developers:
# id vivekOutput:
uid=1122(vivek) gid=1125(vivek) groups=1125(vivek),1124(developers)
Please note that capital G (-G) option add user to a list of supplementary groups. Each group is separated from the next by a comma, with no intervening whitespace. For example, add user jerry to groups admins, ftp, www, and developers, enter:
# useradd -G admins,ftp,www,developers jerry

useradd example - Add a new user to primary group

To add a user tony to group developers use following command:
# useradd -g developers tony
# id tony

Sample outputs:
uid=1123(tony) gid=1124(developers) groups=1124(developers)
Please note that small -g option add user to initial login group (primary group). The group name must exist. A group number must refer to an already existing group.

usermod example - Add a existing user to existing group

Add existing user tony to ftp supplementary/secondary group with usermod command using -a option ~ i.e. add the user to the supplemental group(s). Use only with -G option :
# usermod -a -G ftp tony
Change existing user tony primary group to www:
# usermod -g www tony

Friday, May 13, 2011

How to type New Indian Rupee Symbol(the right way)

To display the Indian rupee symbol , you must have a font—such as the Ubuntu Font Family—with support for the character.
Windows users may use the new Rupkara font which has the Unicode postion mapping for the symbol. For  downloading the font, please visit-http://blog.foradian.com/rupakara-first-font-with-indian-rupee-symbol
For K/Ubuntu 10.10 users, this is automatic.The sign can inserted in your own documents using copy-and-paste from another location, or using the Unicode-entry method, which is the correct way of doing it, and it is as follows-
  • Ubuntu 10.10:20b9
  • MS Windows: 20b9
  • Kubuntu 10.10: Copy-and-paste ‘₹’
  • HTML: insert “₹”
The codepoint at U+20B9 was assigned by the Unicode consortium on 11 August 2010 (2010-08-11).
A fact-
Ubuntu 10.10 is the first operating system to ship with out-of-the-box support for displaying the Indian Rupee Sign, and this happened on 10 October 2010 (2010-10-10).