things to learn in linux

  
Advance administrative tasks on OS linux
  Linux Server, Installation and configuration of Apache, FTP, DNS, DHCP, SAMBA Server,       networking, RAID configuration on LINUX platforms
  Troubleshooting issues of linux Operating System.
  Snapshot based backup technology.
  Build and support complex linux systems of physical and virtual(XEN based).
  experience on another Open Source Hypervisor such as VBox, KVM with experience on P2V,  V2P, BMR
  Backup solutions Veritas / Arc serve / NTBackup.

  large server cluster
  systems automation
  Amazon EC2, SQS, S3
  tools like Puppet, MemCached, Varnish, TokyoCabinet, HAProxy, Nagios, Cacti, Ganglia, and MySQL
  C and Kernel programming, multithreading and synchronization
  Linux kernel, driver development and troubleshooting
  OS concepts, multiprocessing, File Systems, Virtual Memory
  processor architecture, SMP systems, memory hierarchy
  high availability database driven environments.
  Apache HA, High Availability, SAN, DRBD, Load balancing, TCP/IP, database driven environment
  Load Balancing, DRBD, Apache HA,  IP tables,  Web application
  VMWare ESX / vSphere
  RedHat Cluster
  Sun Cluster
  EMC and Hitachi SAN storage and zoning
  Fault Tolerant networking, High Availability
  VMware : Clustering, High Availablity, Dynamic Resource Scheduling
           Storage distribution
           Switches, physical networking
           VMWare Certified Professional
           FibreChannel storage

  Loadbalancers, Packet Filtering, IPFilter, Security, Penetration testing, Break/Fix  
  install, tune, troubleshoot, apply patches and support Web servers and integrate third party applications Responsible for uptime of the Web severs and improving performance

  knowledge in conducting VAPT and providing solutions
  knowledge of source control management.
  Knowledge in ethical hacking and information security management systems
  implementation and maintenance of web analytics
  Apache, Tomcat and IIS web servers administration
  nmap, snmpwalk, nessus, dnswalk, libwhisker, strace
  HP Openview, Nagios, ZenOSS
  Automated Web Application Stress Testing
  Tomcat, and Bea Weblogic java application servers
  openldap, slurpd to syncrepl migration, ldapsearch

  Advanced usage of sniffers for network troubleshooing and optimization
  tcpdump, ethereal, and ngrep all covered indepth
  Linux and Unix proactive system hardening
  tcpdump, ntop, ethereal / wireshark
  Apache Web Server, Bind DNS,

  Vulnerability scanning and network penetration testing of customer facing applications
  Customized and branded Perl open source web metrics reporting software for intranet usage statistics

Useful Linux scripts - lsof, ps, fuser, netstat

Important PS command:

I use the following ps commands in order to check for performance probelms:

1) Displaying top CPU_consuming processes:

ps aux | head -1; ps aux | sort -rn +2 | head -10

2) Displaying top 10 memory-consuming processes:

ps aux | head -1; ps aux | sort -rn +3 | head

3) Displaying process in order of being penalized:

ps -eakl | head -1; ps -eakl | sort -rn +5

4) Displaying process in order of priority:

ps -eakl | sort -n +6 | head

5) Displaying process in order of nice value

ps -eakl | sort -n +7

6) Displaying the process in order of time

ps vx | head -1;ps vx | grep -v PID | sort -rn +3 | head -10

7) Displaying the process in order of real memory use

ps vx | head -1; ps vx | grep -v PID | sort -rn +6 | head -10

8) Displaying the process in order of I/O

ps vx | head -1; ps vx | grep -v PID | sort -rn +4 | head -10

9) Displaying WLM classes

ps -a -o pid, user, class, pcpu, pmem, args

10) Determinimg process ID of wait processes:

ps vg | head -1; ps vg | grep -w wait

11) Wait process bound to CPU

ps -mo THREAD -p <PID>


lsof:

       To list all open files, use:
     
             # lsof

       To list all open Internet, x.25 (HP-UX), and UNIX domain files, use:

        # lsof -i -U

       To list all open IPv4 network files in use by the process whose PID is 1234, use:

             # lsof -i 4 -a -p 1234

       To list all files using any protocol on ports 513, 514, or 515 of host wonderland.cc.purdue.edu, use:

             # lsof -i @wonderland.cc.purdue.edu:513-515

       To list all files using any protocol on any port of mace.cc.purdue.edu (cc.purdue.edu is the default domain), use:

             # lsof -i @mace

       To list all open files for login name ââabeââ, or user ID 1234, or process 456, or process 123, or process 789, use:

             # lsof -p 456,123,789 -u 1234,abe

       To list all open files on device /dev/hd4, use:

             # lsof /dev/hd4


     To find the process that has /u/abe/foo open, use:

             # lsof /u/abe/foo

       To send a SIGHUP to the processes that have /u/abe/bar open, use:

             # kill -HUP âlsof -t /u/abe/barâ

       To find any open file, including an open UNIX domain socket file, with the name /dev/log, use:

             # lsof /dev/log

       To find processes with open files on the NFS file system named /nfs/mount/point whose server  is  inaccessible,  and presuming your mount table supplies the device number for /nfs/mount/point, use:

             # lsof -b /nfs/mount/point

       To do the preceding search with warning messages suppressed, use:

             # lsof -bw /nfs/mount/point

       To ignore the device cache file, use:

             # lsof -Di

       To  obtain  PID  and command name field output for each process, file descriptor, file device number, and file inode number for each file of each process, use:

             # lsof -FpcfDi

       To list the files at descriptors 1 and 3 of every process running the lsof command for login  ID  ââabeââ  every  10  seconds, use:

             # lsof -c lsof -a -d 1 -d 3 -u abe -r10

       To list the current working directory of processes running a command that is exactly four characters long and has an  âoâ or âOâ in character three, use this regular expression form of the -c c option:

             # lsof -c /^..o.$/i -a -d cwd

       To find an IP version 4 socket file by its associated numeric dot-form address, use:

             # lsof -i@128.210.15.17 

fuser:

      # fuser -km /home

kills all processes accessing the file system /home in any way.



      # if fuser -s /dev/ttyS1; then :; else something; fi

invokes something if no other process is using /dev/ttyS1.


      # fuser telnet/tcp shows all processes at the (local) TELNET port.



Some Important Command to find DDOS Attack

netstat -anp |grep 'tcp\|udp' | awk '{print $5}' | cut -d: -f1 | sort | uniq -c | sort -n

netstat -ntu | awk '{print $5}' | cut -d: -f1 | sort | uniq -c | sort -nr

netstat -ntu | grep -v TIME_WAIT | awk '{print $5}' | cut -d: -f1 | sort | uniq -c | sort -nr

netstat -an | grep :80 | awk '{print $5}' | cut -f1 -d":" | sort | uniq -c | sort -n




netstat Command Example

# netstat –listen

Display open ports and established TCP connections:

# netstat -vatn

For UDP port try following command:

# netstat -vaun

If you want to see FQDN then remove -n flag:

# netstat -vat

lsof Command Examples

Display list of open ports

# lsof -i

To display all open files, use:

# lsof

To display all open IPv4 network files in use by the process whose PID is 9255, use:

# lsof -i 4 -a -p 9255


list information about TCP sessions on your server (specifically SSH in this example)
# lsof -i tcp@`hostname`:22

COMMAND  PID USER   FD   TYPE DEVICE SIZE NODE NAME
sshd2   7585 root    5u  IPv4  16105       TCP localbox:ssh->your.src.ip.here:5897 (ESTABLISHED)
sshd2   7653 root    5u  IPv4  16188       TCP localbox:ssh->your.src.ip.here:2262 (ESTABLISHED)

list information about all TCP session
# lsof -i tcp@`hostname`

list information about all sockets using port 53 (will display named information on UDP/TCP)
# lsof -i @`hostname`:53

list information about all UDP sessions
# lsof -i udp@`hostname`

will list all open files with "ssh" in them
# lsof -c ssh

list everything but with UIDs insted of the UID name from /etc/passwd
# lsof -l

list all open files with "ssh" and only the UIDs
# lsof -l -c ssh

list all open files for the /tmp dir (very slow), but good for finding that nasty process that's holding a file open (although:  fuser -m /tmp, will do the same thing)
# lsof +D /tmp



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


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


 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


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


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

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 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





















thing to read

lvm :
http://linuxhelp.blogspot.com/2005/04/creating-lvm-in-linux.html
http://linuxconfig.org/Linux_lvm_-_Logical_Volume_Manager
http://tuxradar.com/content/lvm-made-easy

linux system admin stuff imp :
http://www.yolinux.com/TUTORIALS/LinuxTutorialSysAdmin.html






system admin techniques implemented at slideshare.com

Do you speak native Linux and have operations experience with a large server cluster?
Are you enthusiastic about systems automation (we love Puppet, Chef or CFEngine experience will also give you the right philosophical background)?
 SlideShare is looking for dev-ops engineers who will be responsible for scaling SlideShare to hundreds of servers, using automation, virtualization, and cloud computing technologies like Amazon EC2, SQS, S3 (which we use extensively).
 We don't believe ops should spend all day firefighting and doing chores to keep the system healthy.
 We believe ops should create valuable intellectual property the way software engineers do, using tools like Puppet, MemCached, Varnish, TokyoCabinet, HAProxy, Nagios, Cacti, Ganglia, and MySQL

A Note On Practice And Persistence - Python developer

While you are studying programming, I'm studying how to play guitar. I practice it every day for at least 2 hours a day. I play scales, chords, and arpeggios for an hour at least and then learn music theory, ear training, songs and anything else I can. Some days I study guitar and music for 8 hours because I feel like it and it's fun. To me repetitive practice is natural and just how to learn something. I know that to get good at anything you have to practice every day, even if I suck that day (which is often) or it's difficult. Keep trying and eventually it'll be easier and fun.

As you study this book, and continue with programming, remember that anything worth doing is difficult at first. Maybe you are the kind of person who is afraid of failure so you give up at the first sign of difficulty. Maybe you never learned self-discipline so you can't do anything that's "boring". Maybe you were told that you are "gifted" so you never attempt anything that might make you seem stupid or not a prodigy. Maybe you are competitive and unfairly compare yourself to someone like me who's been programming for 20+ years.

Whatever your reason for wanting to quit, keep at it. Force yourself. If you run into an Extra Credit you can't do, or a lesson you just do not understand, then skip it and come back to it later. Just keep going because with programming there's this very odd thing that happens.

At first, you will not understand anything. It'll be weird, just like with learning any human language. You will struggle with words, and not know what symbols are what, and it'll all be very confusing. Then one day BANG your brain will snap and you will suddenly "get it". If you keep doing the exercises and keep trying to understand them, you will get it. You might not be a master coder, but you will at least understand how programming works.

If you give up, you won't ever reach this point. You will hit the first confusing thing (which is everything at first) and then stop. If you keep trying, keep typing it in, trying to understand it and reading about it, you will eventually get it.

But, if you go through this whole book, and you still do not understand how to code, at least you gave it a shot. You can say you tried your best and a little more and it didn't work out, but at least you tried. You can be proud of that.

career skill set for linux

Systems Software Development Engineer,

* Strong C and Kernel programming, multithreading and synchronization
* Deep understanding of the Linux kernel, driver development and troubleshooting
* Deep understanding of OS concepts, multiprocessing, File Systems, Virtual Memory
* Deep understanding of processor architecture, SMP systems, memory hierarchy
* Knowledge of Storage system concepts will be added advantage
* Good communication skills - technical documentation, code review, reporting results
* Ability to work with co-located as well as distributed teams

Additional:
* Knowledge of IO Buses: PCI-Express, Hypertransport
* Experience working with GNU toolchains, source control (CVS/Subversion)
* Knowledge of BSD Unix will be added advantage


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