How to handle ORA-01000 Error

ORA-01000 maximum open cursors exceeded

Cause: A host language program attempted to open too many cursors. The initialization parameter OPEN_CURSORS determines the maximum number of cursors per user.

Action: Modify the program to use fewer cursors. If this error occurs often, shut down Oracle, increase the value of OPEN_CURSORS, and then restart Oracle.
This error happens a lot in association with some kind of application.
This error also happens at the database level, with just regular inserts, updates, deletes, etc. in PL/SQL or in SQL*Plus, etc.
The reason you receive this error is because Oracle has reached the set limit for open cursors
allowed for that executable or that user session. There are two kinds of open cursors:
implicit and explicit. Here is some background on how cursors work.

To process a SQL statement, Oracle opens a work area called a private SQL area. This private SQL area stores information needed to execute a SQL statement. Cursors are stored in this area to keep track of information. An IMPLICIT cursor is declared for all data definition and data manipulation statements. These are internal to Oracle. For queries that return more than one row, you must declare an EXPLICIT cursor to retrieve all the information. You can tune explicit cursors more easily as you can decide when to open them and close them.

Implicit cursors are harder to tune because they are internal to Oracle. If the application is tuned carefully, it may cut down the number of implicit cursors opened.

Keep in mind that the maximum number of allowed cursors is per session, not per instance.-----

Workarounds

There are two ways to workaround this ORA-01000 error. You can tune cursor usage at the database level and at the application level.

Tuning at the DATABASE LEVEL

There is a parameter you can set in the init.ora that determines the number of cursors a user can open in a session: OPEN_CURSORS.

OPEN_CURSORS by default is 50 and usually, this is not high enough. The highest value you can set this parameter to is operating system dependant. To solve the ORA-01000 error, set the OPEN_CURSORS to a higher number. You may need to set it to the maximum of the operating system limit.

In many systems it is set to 1000 (or even more – 3000, 50000) without any problem. But setting of this parameter to values more than 1000 must be discussed, if there is such need, it will means that something is wrong with the application that leads to that error. Then the application code must be revised instead of changing of this parameter to higher values. Even values more than 300 could be considered as bigger.

Consequences to changing this parameter:This parameter does not affect performance in any way but Oracle will now need a little more memory to store the cursors. It will affect only used memory, not the resources thatOracle will need to support this increased value.

Tuning at the APPLICATION LEVEL

For this level is responsible the development team.

50 UNIX / Linux Sysadmin Tutorials

1. Disk to disk backup using dd command: dd is a powerful UNIX utility, which is used by the Linux kernel makefiles to make boot images. It can also be used to copy data. This article explains how to backup entire hard disk and create an image of a hard disk using dd command.
2. 15 rsync command examples: Every sysadmin should master the usage of rsync. rsync utility is used to synchronize the files and directories from one location to another. First time, rsync replicates the whole content between the source and destination directories. Next time, rsync transfers only the changed blocks or bytes to the destination location, which makes the transfer really fast.
3. Three sysadmin rules: If you are a sysadmin, you can’t (and shouldn’t) break these three sysadmin rules.
4. User and group disk quota: This article explains how to setup user and group quote with soft limit, hard limit and grace period. For example, if you specify 2GB as hard limit, user will not be able to create new files after 2GB.
5. Troubleshoot using dmesg: Using dmesg you can view boot up messages that displays information about the hardware devices that the kernel detects during boot process. This can be helpful during troubleshooting process.
6. RPM package management examples: 15 examples provided in this article explains everything you need to know about managing RPM packages on redhat based system (including CentOS).
7. 10 netstat examples: Netstat command displays various network related information such as network connections, routing tables, interface statistics, masquerade connections, multicast memberships etc.,
8. Manage packages using apt-* commands: These 13 practical examples explains how to manage packages using apt-get, apt-cache, apt-file and dpkg commands.
9. Modprobe command examples: modprobe utility is used to add loadable modules to the Linux kernel. You can also view and remove modules using modprobe command.
10. Ethtool examples: Ethtool utility is used to view and change the ethernet device parameters. These examples will explain how you can manipulate your ethernet NIC card using ethtool.
11. NFS mount using exportfs: This is a linux beginners guide to NFS mount using exportfs. This explains how to export a file system to a remote machine and mount it both temporarily and permanently.
12. Change timezone: Depending on your Linux distribution, use one of the methods explained in this article to change the timezone on your system.
13. Install phpMyAdmin: phpMyAdmin is a web-based tool written in PHP to manage the MySQL database. Apart from viewing the tables (and other db objects), you can perform lot of DBA functions through the web based interface. You can also execute any SQL query from the UI.
14. Setup squid to control internet access: Squid is a proxy caching server. You can use squid to control internet access at work. This guide will give a jump-start on how to setup squid on Linux to restrict internet access in an network.
15. Add new swap space: Use dd, mkswap and swapon commands to add swap space. You can either use a dedicated hard drive partition to add new swap space, or create a swap file on an existing filesystem and use it as swap space.
16. Install and configure snort: Snort is a free lightweight network intrusion detection system for both UNIX and Windows. This article explains how to install snort from source, write rules, and perform basic testing.
17. Register RHEL/OEL linux to support: If you have purchased support from Oracle for your Linux, you can register to oracle support network (ULN) using up2date as explained here.
18. tftpboot setup: You can install Linux from network using PXE by installing and configuring tftpboot server as explained here.
19. Delete all iptables rules: When you are starting to setup iptables, you might want to delete (flush) all the existing iptables as shown here.
20. Disable ping replies: Someone can flood the network with ping -f. If ping reply is disabled as explained here we can avoid this flooding.
21. Block ip address using fail2ban: Fail2ban is a intrusion preventon framework that scans log files for various services ( SSH, FTP, SMTP, Apache, etc., ) and bans the IP that makes too many password failures. It also updates iptles firewall rules to reject these ip addresses.
22. Package management using dpkg: On debian, you can install or remove deb packages using dpkg utility.
23. Alfresco content management system: Alfresco is the best open source content management system. Everything you need to know to install and configure Alfresco is explained here.
24. Bugzilla bug tracking system: Bugzilla is the best open source bug tracking system. Everything you need to know to install and configure Bugzilla is explained here.
25. Rpm, deb, dpot and msi packages: This article explains how to view and extract files from various package types used by different Linux / UNIX distributions.
26. Backup using rsnapshot: You can backup either a local host or remote host using rsnapshot rsync utility. rsnapshot uses the combination of rsync and hard links to maintain full-backup and incremental backups. Once you’ve setup and configured rsnapshot, there is absolutely no maintenance involved in it. rsnapshot will automatically take care of deleting and rotating the old backups.
27. Create Linux user: This article explains how to create users with default configuration, create users with custom configuration, create users interactively, and creating users in bulk.
28. Mount and view ISO file: ISO files are typically used to distribute the operating system. Most of the linux operating system that you download will be on ISO format. This explains how to view and mount any ISO file both as regular use and as root user.
29. Manage password expiration and aging: Linux chage command can be used to perform several practical password aging activities including how-to force users to change their password.
30. ifconfig examples: Interface configurator command ifconfig is used to initialize the network interface and to enable or disable the interfaces as shown in these 7 examples.
31. Oracle db startup an sthudown: Every sysadmin should know some basic DBA operations. This explains how to shutdown and start the oracle database.
32. PostgreSQL install and configure: Similar to mySQL, postgreSQL is very famous and feature packed free and open source database. This is a jumpstart guide to install and configure postgresql from source on Linux.
33. Magic SysRq key: Have you wondered what the SysRq key on your keyboard does. Here is one use for it. You can safely reboot Linux using the magic SysRq key as explained here.
34. Wakeonlan Tutorial: Using Wakeonlan WOL, you can turn on the remote servers where you don’t have physical access to press the power button.
35. List hardware spec using lshw: ls+hw = lshw, which lists the hardware specs of your system.
36. View hardware spec using dmidecode: dmidecode command reads the system DMI table to display hardware and BIOS information of the server. Apart from getting current configuration of the system, you can also get information about maximum supported configuration of the system using dmidecode. For example, dmidecode gives both the current RAM on the system and the maximum RAM supported by the system.
37. Use the support effectively: Companies spend lot of cash on support mainly for two reasons: 1) To get help from vendors to fix critical production issues 2) To keep up-to-date with the latest version of the software and security patches released by the vendors. In this article, I’ve given 10 practical tips for DBAs, sysadmins and developers to use their hardware and software support effectively.
38. Install/Upgrade LAMP using Yum: Installing LAMP stack using yum is a good option for beginners who don’t feel comfortable installing from source. Also, Installing LAMP stack using yum is a good choice, if you want to keep things simple and just use the default configuration.
39. Template to track your hardware assests: If you are managing more than one equipment in your organization, it is very important to document and track ALL information about the servers effectively. In this article, I have listed 36 attributes that needs to be tracked for your equipments, with an explanation on why it needs to be tracked. I have also provided a spreadsheet template with these fields that will give you a jumpstart.
40. Disable SELinux: If you don’t understand how SELinux works and the fundamental details on how to configure it, keeping it enabled will cause lot of issues. Until you understand the implementation details of SELinux you may want to disable it to avoid some unnecessary issues as explained here.
41. Install PHP5 from source: This is a step-by-step guide to install PHP5 from source on UNIX environment.
42. Install MySQL from source: This is a step-by-step guide to install MySQL from source on UNIX environment.
43. Launch Linux clients on windows: If you are using SSH client to connect to Linux server from your Windows laptop, sometimes it may be necessary to launch UI application on the remote Linux server, but to display the UI on the windows laptop. Cygwin can be used to install software on Linux from Windows and launch Linux X client software on Windows.
44. IPCS: IPC allows the processes to communicate with each another. The process can also communicate by having a file accessible to both the processes. Processes can open, and read/write the file, which requires lot of I/O operation that consumes time. This explains different types of IPCS and provides 10 IPCS command examples.
45. Logical Volume Manager: Using LVM we can create logical partitions that can span across one or more physical hard drives.You can create and manage LVM using vgcreate, lvcreate, and lvextend lvm2 commands as shown here.
46. 15 Tcpdump examples: tcpdump is a network packet analyzer. tcpdump allows us to save the packets that are captured, so that we can use it for future analysis. The saved file can be viewed by the same tcpdump command. We can also use open source software like wireshark to read the tcpdump pcap files.
47. Manage partition using fdisk: Using fdisk you can create a maximum of four primary partition, delete an existing partition, or change existing partition. Using fidsk you are allowed to create a maximum of four primary partition, and any number of logical partitions, based on the size of the disk.
48. VMWare fundamentals: At some point every sysadmin should deal with virtualization. VMWare is a very popular choise to virtualize your server environment. This article will provide the fundamental information for you to get a jumpstart on VMWare.
49. Rotate the logs automatically: Manging log files is an importat part of sysadmin life. logrotate make it easy by allowing you to setup automatica log rotation based on several configurations. Using logrotate you can also configure it to execute custom shell scripts immediately after log rotation.
50. Passwordless SSH login setup: Using ssh-keygen and ssh-copy-id you can setup passwordless login to remote Linux server. ssh-keygen creates the public and private keys. ssh-copy-id copies the local-host’s public key to the remote-host’s authorized_keys file.

20 Linux System Monitoring Tools Every SysAdmin Should Know

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.

#1: top - Process Activity 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    10.1.3.145       14:55    5.00s  0.04s  0.02s vim /etc/resolv.conf

root     pts/1    10.1.3.145       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
Output:

 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:

  PID TTY          TIME CMD

    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=
OR
# pgrep lighttpd
OR
# 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.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 -="-" amp="amp" tcp="tcp" xf0="xf0">>2)) != 0)'
To display all FTP session to 202.54.1.5, enter:
# tcpdump -i eth1 'dst 202.54.1.5 and (port 21 or 20'
To display all HTTP session to 192.168.1.5:
# tcpdump -ni eth0 'dst 192.168.1.5 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 {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

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.