Month: October 2011

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Important /Required Monitoring Tools/ Commands For Linux System Administrators

Hi Guys,

First of all thank you for for your love and support. In this article I’m trying to post my knowledge and experience about Linux server monitoring. As a system administrator it is essential to have good knowledge about monitoring weapons so you can keep your server calm and cool and can get better performance through it. so lets start::

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 – Display Linux tasks

top provides an ongoing look at processor activity in real time. It displays a listing of the most CPU-intensive tasks on the system, and can provide an interactive interface for manipulating processes. It can sort the tasks by CPU usage, memory usage and runtime. can be better configured than the standard top from the procps suite

Commonly Used Hot Keys

Friends, I always recommend to use all available tools/options with simple commands, so try below keys with “top” command.

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 – Report virtual memory statistics

This command reports information about the kernel threads, virtual memory, disks, 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
See Memory Utilization Slabinfo
    # vmstat -m
    Cache                       Num  Total   Size  Pages
ip_conntrack_expect           0      0    136     28
ip_conntrack               8048  11856    304     13
ip_fib_alias                 50    118     64     59
ip_fib_hash                  42    118     64     59
iser_descriptors              0      0    128     30
ib_mad                        0      0    448      8
jbd_1k                        0      0   1024      4
bio_map_info                100    105   1064      7
dm_mpath                      0      0   1064      7
jbd_4k                       26     48   4096      1
dm_uevent                     0      0   2608      3
dm_tio                        0      0     24    144
dm_io                         0      0     40     92
scsi_cmd_cache              143    170    384     10
sgpool-128                   32     34   4096      1

#3: w – Display Logged in Sessions

we command displays information about the users currently on the machine, and their processes.

    root@linuxserverguide [~]# w
 09:17:33 up 18 days, 20:50,  1 user,  load average: 2.57, 2.61, 2.45
USER     TTY      FROM              LOGIN@   IDLE   JCPU   PCPU WHAT
root     pts/1    192.168.1.1   06:42    0.00s  0.06s  0.00s w

#4: uptime – Display system uptime

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.

    root@linuxserverguide [~]# 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 – Display Process Stats


ps command will report a snapshot of the current processes. To select all processes use the -A or -e option:


    

    root@linuxserverguide [~]# 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


    

    root@linuxserverguide [~]# ps -Al
    

    F S   UID   PID  PPID  C PRI  NI ADDR SZ WCHAN  TTY          TIME CMD
4 S     0     1     0  0  75   0 -  2592 -      ?        00:00:00 init
1 S     0     2     1  0 -40   - -     0 migrat ?        00:00:02 migration/0
1 S     0     3     1  0  94  19 -     0 ksofti ?        00:00:01 ksoftirqd/0
5 S     0     4     1  0 -40   - -     0 watchd ?        00:00:00 watchdog/0
1 S     0     5     1  0 -40   - -     0 migrat ?        00:00:01 migration/1
1 S     0     6     1  0  94  19 -     0 ksofti ?        00:00:00 ksoftirqd/1
5 S     0     7     1  0 -40   - -     0 watchd ?        00:00:00 watchdog/1
1 S     0     8     1  0 -40   - -     0 migrat ?        00:00:00 migration/2
    



#6: free – Display Memory Usage


Please see below output carefully, you will find used and free memory by system also it shows buffered memory used by kernel.


    

    root@linuxserverguide [~]# 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 – Display Disk Activity


Friends, this is very powerful command which shows CPU avarage load and disk activity simultaneously, see the sample output below to understand it better


    

    root@linuxserverguide [~]# 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 – Display System Activity


The sar command is used to collect, report, and save system activity information. To see network counter, enter:


    

    root@linuxserverguide [~]#sar -n DEV | more
    

    To display the network counters from the 24th:

    

    root@linuxserverguide [~]# sar -n DEV -f /var/log/sa/sa24 | more
    

    You can also display real time usage using sar:

    

    root@linuxserverguide [~]# 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:


     root@linuxserverguide [~]# 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
    



 

			

			
						

	
	



			
				



	
	


		
					

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It is required that you store all your data in Unicode format (UTF-8), while installing Moodle 2.0

	


		

		
” It is required that you store all your data in Unicode format (UTF-8), while installing Moodle 2.0 ”


Getting error message while Installing Moodle 2.0


It is required that you store all your data in Unicode format (UTF-8). New installations must be performed into databases that have their default character set as Unicode. If you are upgrading, you should perform the UTF-8 migration process (see the Admin page).




Solution:


1. Open your Moodle database which you created in MySQL using phpMyAdmin




2. Run


ALTER DATABASE mydatabasename charset=utf8;


MyDataBaseName= Your Moodle database




3. No more error message saying 


It is required that you store all your data in Unicode format (UTF-8). New installations must be performed into databases that have their default character set as Unicode. If you are upgrading, you should perform the UTF-8 migration process (see the Admin page).





		
	
			

	
	



			
				



	
	


		
					

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How to install mod_evasive on a cPanel server

	


		

		
We are going to install mod_evasive to help protect our cPanel server from low end ddos attacks.  The installation is really quite simple.


This module instantiates for each listener individually, and therefore has a built-in cleanup mechanism and scaling capabilities. Because of this per-child design, legitimate requests are never compromised (even from proxies and NAT addresses) but only scripted attacks. Even a user repeatedly clicking on ‘reload’ should not be affected unless they do it maliciously. mod_evasive is fully tweakable through the Apache configuration file, easy to incorporate into your web server, and easy to us.


OK, now that’s done, how do we install this thing?  Pretty simple, lets log into a terminal session as root.


I always download everything to my downloads folder, so, we change to it:


    root@linuxserverguide[~] # cd downloads


Now, we need to grab the file (this is the latest version as of this post):



Of course, we now need to extract them:


    root@linuxserverguide[~/downloads] # tar zxvf mod_evasive_1.10.1.tar.gz


Now, change into the directory that was just created:


    root@linuxserverguide[~/downloads] #cd mod_evasive


Now, you can view the README file for information on how to install this on a couple of different types of servers, however, we are going to focus on installing mod_evasive on an Apache2x server.  We also have cPanel running on this box, so, to install, we run the following:


    root@linuxserverguide[~/downloads] #/usr/local/apache/bin/apxs -i -a -c mod_evasive20.c


Now, that will create an entry in the httpd.conf file, and, if we want to retain that after an upgrade/rebuild, we need to tell cPanel not to take it out!  Do do this, we now run this:


    root@linuxserverguide[~/downloads] # /usr/local/cpanel/bin/apache_conf_distiller –update


Now, to change the settings for mod_evasive, we need to add them in some place.  All we have done so far, is install the actually module into apache, and, even with a restart, it would not be using it.  So, I like to add things into my includes files through either WHM, or, directly through the terminal.  To do this, we run the following:


    root@linuxserverguide[~/downloads] # vim /usr/local/apache/conf/includes/post_virtualhost_2.conf


Once the file is open, lets add in the following lines to the bottom of the file:


    <IfModule mod_evasive20.c>
    
DOSHashTableSize    3097
    
DOSPageCount        2
    
DOSSiteCount        50
    
DOSPageInterval     1
    
DOSSiteInterval     1
    
DOSBlockingPeriod   3600
    
DOSEmailNotify      root
    
</IfModule>


Once done, save the file, this varies depending on your editor of choice, in VI and VIM, its :wq enter.


That’s all folks!  This will help to lesson the load on your server under a mild ddos attack, or, someone just being silly and trying to increase the load on your server.