IPTABLES

Replace IP-ADDRESS with actual IP address. For example if you wish to block ip address 65.55.44.100 for whatever reason then type command as follows:
# iptables -A INPUT -s 65.55.44.100 -j DROP ================================================ If you just want to block access to one port from an ip 65.55.44.100 to port 25 then type command:
# iptables -A INPUT -s 65.55.44.100 -p tcp --destination-port 25 -j DROP =================================================== TO REMOVE THE BLOCKED IP FROM FIREWALL

1) Login into the server via shell access.
2) Go to the path of APF firewall. It should be:
/etc/csf
3) Edit the file csf.deny.
vi csf.deny
4) Remove the IP address from the list and save the file to unblock the IP address.

Once the IP address removed one need to restart the Firewall…To Restart Firewall one need to execute below mentioned command:

csf -r
===============================================================================

# LFD----CSF
############
/var/log/lfd.log
/etc/init.d/csf restart
tail -f /usr/local/apache/logs/error_log
/etc/init.d/lfd restart
crontab -l
rm -fv /etc/csf/csf.error
iptables -L -n | grep 72.29.86.55
service chkservd restart > restart service after done any in csf
csf -v
csf -x > disable
csf -e >enable

suspicious process

Problem: suspecious process working in server
________________________________________________________________________________________________
For this we have to kill the process or kill the ip given by the user
firewall is situated in /etc/csf
csf.pignor---->is used for bloking process
csf.ignore---->is used for blocking ip address
______________________________
after this restart lfd, and csf
etc/init.d/ csf restart
etc/init.d/ lfd restart
_____________________________________________________________________________________________________
if md5 comparison test is failed is due to the upgradation of the server files
It will check all the files which is modified
to remove this problem go vi /etc/csf/csf.conf
in it change LF_integrity= to 0
.........

swap file creating

when some programs consume huge amount of virtual memory, make use of temporary SWAP space.
This can be achieved by mkswap and swapon

* For EG: To have 64 MB extra swap space

dd if=/dev/zero of=/swapfile bs=1024 count=65535
mkswap /swapfile
swapon /swapfile

where “/swapfile” is the swap filename. The location of this file depends on the availabilty of File System’s Space and the write permission.

when you dont need this anymore, remove it using the following commands

swapoff /swapfile
rm /swapfile

Error from domain wrapper: domainname.com is owned by another user

I got this error when I was trying to add subdomains to one of my cPanel accounts. This happens when cPanel doesn’t remove the subdomain correctly and then it thinks it’s still there so when you try to add it back on you get an error. Here’s how to fix it:

1. Remove domain.com from /var/cpanel/users/cpanel-username

3. Run /scripts/updateuserdomains as root user on the server because you changed the above file manually, this will create adjusted cache files

2. Remove /var/named/domain.com.db if the file exists (it doesn’t always)

3. Remove the virtualhost for domain.com on /usr/local/apache/conf/httpd.conf

4. Remove domain.com from /etc/named.conf

Now you can add the domain back on in cPanel with no problems.

20 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.

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

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

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.

Sample Output:

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.

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.

How do I find out Linux Resource utilization

vmstat command reports information about processes, memory, paging, block IO, traps, and cpu activity. However, a real advantage of vmstat command output - is to the point and (concise) easy to read/understand. The output of vmstat command use to help identify system bottlenecks. Please note that Linux vmstat does not count itself as a running process.

Here is an output of vmstat command from my enterprise grade system:

$ vmstat -S M

procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
r  b   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy id wa
3  0      0   1963    607   2359    0    0     0     0    0     1 32  0 68  0

Where,

• The fist line is nothing but six different categories. The second line gives more information about each category. This second line gives all data you need.
• -S M: vmstat lets you choose units (k, K, m, M) default is K (1024 bytes) in the default mode. I am using M since this system has over 4 GB memory. Without -M option it will use K as unit

Field Description For Vm Mode

(a) procs is the process-related fields are:

• r: The number of processes waiting for run time.
• b: The number of processes in uninterruptible sleep.

(b) memory is the memory-related fields are:

• swpd: the amount of virtual memory used.
• free: the amount of idle memory.
• buff: the amount of memory used as buffers.
• cache: the amount of memory used as cache.

(c) swap is swap-related fields are:

• si: Amount of memory swapped in from disk (/s).
• so: Amount of memory swapped to disk (/s).

(d) io is the I/O-related fields are:

• bi: Blocks received from a block device (blocks/s).
• bo: Blocks sent to a block device (blocks/s).

(e) system is the system-related fields are:

• in: The number of interrupts per second, including the clock.
• cs: The number of context switches per second.

(f) cpu is the CPU-related fields are:

These are percentages of total CPU time.

• us: Time spent running non-kernel code. (user time, including nice time)
• sy: Time spent running kernel code. (system time)
• id: Time spent idle. Prior to Linux 2.5.41, this includes IO-wait time.
• wa: Time spent waiting for IO. Prior to Linux 2.5.41, shown as zero.

As you see the first output produced gives averages data since the last reboot. Additional reports give information on a sampling period of length delay. You need to sample data using delays i.e. collect data by setting intervals. For example collect data every 2 seconds (or collect data every 2 second 5 times only):

Role Of A Sustem Administrator

The person who is responsible for setting up and maintaining the system is called as the system administrator. System administrators may be members of an information technology department. Most of the following discussion also applies to network and Windows system admins.

Duties of a system administrator

The duties of a system administrator are wide-ranging, and vary widely from one organization to another. Sysadmins are usually charged with installing, supporting, and maintaining servers or other computer systems, and planning for and responding to service outages and other problems. Other duties may include scripting or light programming, project management for systems-related projects.

The system administrator is responsible for following things:

1. User administration (setup and maintaining account)
2. Maintaining system
3. Verify that peripherals are working properly
4. Quickly arrange repair for hardware in occasion of hardware failure
5. Monitor system performance
6. Create file systems
7. Install software
8. Create a backup and recover policy
9. Monitor network communication
10. Update system as soon as new version of OS and application software comes out
11. Implement the policies for the use of the computer system and network
12. Setup security policies for users. A sysadmin must have a strong grasp of computer security (e.g. firewalls and intrusion detection systems).