getopts in shell programming

getopts is shell builtin command is used to parse command line arguments.

getopts takes an option string as an argument. The option string is as follows

• Simple flag with no arguments - Just the letter of the flag like say for example, "-f" 
• Flag with arguments - Letter of the flag followed by a colon. Say for example, if something like "-f filename", we would add "f:" to the option string.

getopts also supports detection of unknown flags and missing arguments. To enable this option, a colon(:) should be added as the first character of the option string.

The getopts returns a colon when it encounters a flag with missing argument.
getopts routine returns a question mark when it encounters an unknown flag.

getopts will set an exit status of FALSE when there is nothing left to parse. So it is easier to use getopts in a while loop

while getopts …; do
   …
done

getopts will parse options and their possible arguments. It will stop parsing on the first non-option argument (a string that doesn't begin with a hyphen (-), a string that isn't an argument for an option in front of it). It will also stop parsing when it sees the -- (double-hyphen), which stands for ends of options.

Variables associated with getopts

• OPTIND - It holds the index of the next argument to be processed. OPTIND is initially set to 1, and should be reset to 1 if we need to parse anything again with getopts.
• OPTARG - The argument value associated with the current flag(if any).
• OPTERR - It takes values 0 or 1. It indicates if bash shell should display error messages generated by getopts built-in.  If this variable is set to 1, error reporting by the underlying getopts function is enabled. If set to 0, error reporting is disabled. This variable is ignored if the first character of the option string is a colon(:), which tells getopts that the script can handle and report errors.

Let us demonstrate with following example

#!/bin/bash

while getopts ":f" opt

do

   if [ $opt = "f" ]

   then

         echo "-f was triggered"

   fi

   if [ $opt = "?" ]

   then

         echo "Invalid option flag: -$OPTARG"

         #exit 1

   fi

done 

Calling it without arguments

$ ./opt.sh

$ 

getopts did not see any valid or invalid options

Calling with non option arguments

$ ./opt.sh /etc/passwd

$

Again, getopts did not see any valid or invalid options

Calling with option arguments

$ ./opt.sh -f

-f was triggered

The "f" was put into variable $opt

Suppose an invalid argument is passed as an argument

$ ./opt.sh -a

Invalid option flag: -a

getopts did not accept the option "a" and acted by putting ? into $opt and the invalid option character(a) into $OPTARG.

It is possible to mix valid and invalid options

$ ./opt.sh -a -b -f -c

Invalid option flag: -a

Invalid option flag: -b

-f was triggered

Invalid option flag: -c

It is also possible to give valid option multiple times

$ ./opt.sh -f -f -f

-f was triggered

-f was triggered

-f was triggered

Now let us consider passing arguments for flags

Arguments can be passed to flags by placing a colon(:) after the flag

#!/bin/bash

while getopts ":f:" opt
do
   if [ $opt = "f" ]
   then
         echo "-f was triggered with parameter $OPTARG"
   fi
   if [ $opt = "?" ]
   then
         echo "Invalid option flag: -$OPTARG"
         #exit 1
   fi
   if [ $opt = ":" ]
   then 
         echo "Option flag $OPTARG requires an argument"
   fi
done 

Calling without an argument for the flag

$ ./optarg.sh -f
Option flag f requires an argument

Calling with a valid argument for the flag

$ ./optarg.sh -f /etc/passwd
-f was triggered with parameter /etc/passwd

Double Parantheses (( )) and Single Parantheses () in Bash shell

Let us see what is the difference between double parantheses - (( )) and single parantheses - $() in Bash shell.

Double parantheses is used as math operator in Bash shell. Double parantheses can be used as an extension for numerical for loops. This can be demonstrated as follows

for (( i = 1; i <= 10; i++ ))
do
      echo "$i"
done

$ abc=5
$ echo $((abc-1))
$ 4

Let us come to single parantheses now. What does $() operator stand for - For inline execution. The $() operator inserts the output of one command into the middle of a statement.The Bourne shell provides two operators for executing a command and placing its output in the middle of another command or string. These operators are the $() operator and the backtick (`) operator middle of a statement. This is demonstrated as

$ xyz=$(date)
$ echo $xyz
Tue Dec 25 20:56:30 GMT 2012

$ abc=`date`
$ echo $abc
Tue Dec 25 20:56:15 GMT 2012

Bash Shell : .bash_profile and .bashrc

Whenever a new shell is run, to set environment variables, aliases and export them automatically, the following files come handy

• ~/.bash_profile - executed automatically for all login shells
• ~/.bashrc - executed automatically for all non-login shells ( when bash is explicitly typed on the command line or when a script that starts with #!/bin/bash is run )

We may also find .bashrc file which sources .bash_profile, as follows

. $HOME/.bash_profile

Shell Arithmetic using expr

• shell treats all shell variables as strings.
• shell uses the expr command  to  perform integer arithmetic.
• expr command cannot do real or non-integer arithmetic.
• expr takes two integer arguments and an operand and writes the result to the standard output. If the output need to be stored in a variable, command substitution(`) need to be used.

$ expr 1 + 1

2

$ a=`expr 1 + 1`

$ echo $a

2

There must be spaces between the operand and the arguments.

Note: * is the multiplication operand. But * has special meaning to the shell. Hence while using *, it should be shielded using \ character.

$ expr 2 \* 2

4

Positional parameters and Accessing all positional parameters in Shell

The positional parameters in shell are specified by parameters from $1 to $9.
To list all the positional parameters shell provides two variables : $* and $@
When not quoted, these two variables are equivalent.

However, when these variables are quoted, "$*" and "$@", they behave differently. Let us illustrate with following example

Suppose, I have two files named 'first file' and 'second file'.
I want to cat the output of two files.
These two files have space in their names.

"$*" when quoted, does not take into account any special quoting in the file names when the files are passed as parameters(here, it does not take into account the space in the file names). So $* when quoted produces a single string of all positional parameters.

But "$@" will preserve the special quoting(space in the file names, in this example). "$@" when quoted, produces a list of positional parameters.

Let us see what happens when we use $*, $@, "$*", "$@" to specify the positional parameters first file and second file

#/bin/bash
#pos.sh
cat $*

$ ./pos.sh first\ file second\ file
cat: first: No such file or directory
cat: file: No such file or directory
cat: second: No such file or directory
cat: file: No such file or directory

#/bin/bash
#pos.sh
cat $@

$ ./pos.sh first\ file second\ file
cat: first: No such file or directory
cat: file: No such file or directory
cat: second: No such file or directory
cat: file: No such file or directory

#!/bin/bash
#pos.sh
cat "$*"

$ ./pos.sh first\ file second\ file
cat: first file second file: No such file or directory

#!/bin/bash
#pos.sh
cat "$@"

$ ./pos.sh first\ file second\ file
abc
xyz

In this case, the output of first file and second file get concatenated  successfully.

CPU Caches

Each CPU has it's own cache. Each cache has it's own associated cache controller. Data must be in CPU cache before the work can begin.

Cache memory is organized into lines. Each line of cache can be used to cache a specific location in memory.

A cache may be for

• instructions for the processors, the I-cache
• data, the D-cache
• both instructions and data

Cache Hit

When the CPU makes a reference to the main memory, the cache controller first checks to see if the requested address is in cache. If the requested memory is in cache it is referred as cache-hit.

Cache Miss

When the CPU makes a reference to the main memory, and if the cache controller does not see the requested address in cache, then a cache-miss occurs.

Cache Line Fill

When a cache-miss occurs, the requested memory location must be read from main memory and brought into cache. The process of moving data from RAM to cache is this known as cache line fill.

The processor both reads and writes into cache memory. So when something is written to cache, it must be updated in main memory(RAM) too. The write operation can be configured in two ways

• write-through
• write-back

If write-through caching is enabled, then when a particular line of cache is updated, the corresponding location in memory is updated as well.

If write-back caching is enabled, a write to cache line does not get written back to main memory until the cache line is deallocated.

write-back caching is more efficient than write-through caching.

CPU Cache Types

• Direct Mapped Cache : This is the least expensive type of cache memory. Each line of direct mapped cache can only cache a specific location in memory.
• Fully Associatve Cache Memory : Most flexible type of cache memory and consequently the most expensive one. In fully associative cache, a line can cache any location in main memory.
• Set Associative Cache Memory : Set associative memory provides a good compromise between direct mapped cache and fully associative cache. Most systems use this type of cache. Set associative cache memory is usually referred to as n-way set associative where n is some power of 2. Set associative cache memory allows a memory location to be cached into any one of the n lines of cache.

There can be multiple levels of cache, like L1, L2.

To calculate cache in our system

# x86info -c

Found 2 CPUs

--------------------------------------------------------------------------

CPU #1

Cache info

 L1 Instruction cache: 32KB, 8-way associative. 64 byte line size.

 L1 Data cache: 32KB, 8-way associative. 64 byte line size.

 L2 cache: 1MB, sectored, 8-way associative. 64 byte line size.

--------------------------------------------------------------------------

CPU #2

Cache info

 L1 Instruction cache: 32KB, 8-way associative. 64 byte line size.

 L1 Data cache: 32KB, 8-way associative. 64 byte line size.

 L2 cache: 1MB, sectored, 8-way associative. 64 byte line size.

# getconf -a | grep -i cache

LEVEL1_ICACHE_SIZE                 32768

LEVEL1_ICACHE_ASSOC                8

LEVEL1_ICACHE_LINESIZE             64

LEVEL1_DCACHE_SIZE                 32768

LEVEL1_DCACHE_ASSOC                8

LEVEL1_DCACHE_LINESIZE             64

LEVEL2_CACHE_SIZE                  1048576

LEVEL2_CACHE_ASSOC                 8

LEVEL2_CACHE_LINESIZE              64

LEVEL3_CACHE_SIZE                  0

LEVEL3_CACHE_ASSOC                 0

LEVEL3_CACHE_LINESIZE              0

LEVEL4_CACHE_SIZE                  0

LEVEL4_CACHE_ASSOC                 0

Profiling Cache Usage using valgrind

The following command helps in simulating cache usage

# valgrind --tool=cachegrind <programname>

Apache Memory Leak and MaxRequestsPerChild

In many cases. Apache will leak memory. Because of memory leak, Apache will not be able to fork new child processes to serve new requests. However httpd still can answer requests with pre-allocated memory.

To solve this memory leak in Apache, usually we need to restart Apache service to free up memory. In case of frequent memory leaks, to restart the Apache 

1. We can set a cron job to restart apache every "n" hours Or
2. If logrotation is in place for Apache, during logrotation of Apache log files, the memory will get freed up

However, an effective way to deal with Apache memory leak is by setting an appropriate value for MaxRequestsPerChild directive in Apache.

MaxRequestsPerChild:

The MaxRequestsPerChild directive sets the limit on the number of requests that an individual child server process will handle. After MaxRequestsPerChild requests, the child process will die. 

It is set to 0 by default, the child process will never expire. It is appropriate to set this to a value of few thousands. This can help prevent memory leakage, since the process dies after serving a certain number of requests. Don't set this too low, since creating new processes does have overhead.

For example, set MaxRequestsPerChild 2000 in Apache conf file. Means that after 2000 requests the worker process is shut down and therefore frees up the memory it leaked and locked before.

Bash Socket Programming : Scan ports using Bash shell's /dev/tcp

In bash shell, a network socket can be opened to pass data through it.
A tcp socket as well as a udp socket can be opened using either of the following

• /dev/tcp/host/port - The host should be a valid hostname or Internet address, and port should be an integer number or service name. bash attempts to open a TCP connection to the corresponding socket.
• /dev/udp/host/port - The host shall be a valid hostname or Internet address, and port shall be an integer port number or service name. bash attempts to open a UDP connection to the corresponding socket.

Let us see how to use it for port scanning. Say for example, if we need to find if port 80 is open or closed for google.com, run the following command

$ echo >/dev/tcp/google.com/80 && echo "port 80 is open" || echo "port 80 is closed"

In case if the port is open, the output is received quickly. However, if the port is closed, it takes a long time to get an output.
So we can use the "timeout" utility to  exit the command in case the response is not received within specified time limit.

$ timeout 1 bash -c "echo >/dev/tcp/$host/$port" && echo "port $port is open" || echo "port $port is closed"

•  bash -c : If the -c option is present,  then  commands  are  read from the string. 

To scan a range of ports, say for example port 1 to 100, do the following

for port in {1..100}
do
    timeout 1 bash -c "echo >/dev/tcp/google.com/$port" && echo "port $port is open" || echo "port $port is closed"
done

AWK Tip - Remove duplicate lines without sorting file

Remove duplicate lines without having to sort file

awk '!a[$0]++'  <file>

SNMP

SNMP (Simple Network Management Protocol) is an application layer protocol on TCP/IP network that facilitates the exchange of management information between network devices. SNMP is an industry standard way to gather information from hosts across a network.

SNMP works on a standard client/server model. The SNMP client/or agent, sends a request across the network to a host running SNMP server. The SNMP server, snmpd, then gathers the information from the local system and returns it to the client/agent. Each SNMP server has a list of information(or objects) it can extract from the local computer. This list of information is arranged in a hierarchical system called, Management Information Base(MIB) tree. So basically, the SNMP agent/client accesses the MIB on the server to fetch an object. An object corresponds to a particular information about the device(server) - say for example, swap usage, uptime and so on. An SNMP agent can also send a request to make changes to the SNMP server.

The objects in a server are fetched, managed by client/agent using the following four fundamental operations - Get, GetNext, Set, Trap

1. The client or agent, sends a Get command to fetch an object from the host running snmpd server. This object shall be leaf node in the MIB
2. The client or agent, can recursively retrieve objects from the host running snmpd server, using GetNext command. The GetNext operates on a branch in MIB
3. The client or agent, can control the server by using the Set command to change the value of an object
4. If the server needs to notify the client/agent of some event, server can issue an Trap command to pass the message to the client/agent.

A system can function as a client/agent or a server or both.

SNMP can be used in 3 versions - v1, v2, v3

SNMP v1 relies on a simple string , called the community name to provide security. Two community names are used - public and private. In a default configuration, the public community is used to provide read access to a managed device while the private community is used to allow read-write access. All information exchanged between the client/agent and server are sent in clear text. In case if we are using SNMP v1, as a simple security measure, use alternative names for public and private.

SNMP v2 has some inconsistent implementations. So skipping it.

SNMP v3 provides three very important security features:

1. Usernames to audit SNMP connections made to server
2. Passwords to allow authenticated access to server
3. Encryptions allows data to be exchanged between server and client/agent securely

Management Information Base(MIB)

Each object in a MIB tree is identified by a name or number. Since, it is a tree structure(like unix), each object in MIB tree can be reached by following a unique path for that object(same like unix path).

Consider the following example of an MIB object. MIB object name, is it's path in the MIB tree, like follows

• interfaces.ifTable.ifEntry.ifOutErrors.1
• interfaces, means that we are looking at the network interfaces on the system(network cards, parallel ports, and so on).
• ifTables, is the interface table  or the list of interfaces on the system
• ifEntry, shows one particular interface
• ifOutErrors, means that we are looking at the outbound errors on this particular interface
• 1, means that we are interested in interface number 1.

MIB objects can also be expressed as numbers and the preceding example can be translated to numbers as follows

•  .1.3.6.1.2.1.2.2.1.20.1

This is also called as arc.

Expressed as words, the MIB object is specified as five terms separated by periods. Expressed as numbers, the MIB has 11. So why it is like this?

The numerical MIB is longer because it includes the default .1.3.6.1.2.1 (.iso.org.dod.internet.mgmt.mib-2). Almost all MIBs,will have this leading string.

Setting up snmp client

Check if net-snmp-utils package is installed

# yum list all | grep snmp

If not installed, then install

# yum search snmp

# yum install net-snmp-utils

Setting up snmp server

yum install net-snmp

yum install net-snmp-utils

Finding MIB object

• Tree Browse

     snmptranslate -TB '.*memory.*'

• Output numerical

snmptranslate -On HOST-RESOURCES-MIB::hrMemorySize

• Tree print with Output Full

snmptranslate -Tp -Of .1.3.6.1.2.1.25

Using SNMP v1 for queries

From my host 192.168.1.3, suppose I want to query the objects on 192.168.2.101, using the "public" string of snmp v1

Using snmpwalk command, I shall use the "public" string of snmp v1 to get a list of objects I can access on 192.168.2.101

# snmpwalk -v1 -c public 192.168.2.101

Instead of using community name as "public", you can use your own community string name, say "myu" for example. To set your own community string in 192.168.2.101, do the following

1. Open /etc/snmp/snmpd.conf in 192.168.2.101
2. Add the following line at end of the file -  rocommunity myu
3. service snmpd reload

Now obtain the contents of the MIB tree in 192.168.2.101 using the community string "myu", by running the following command from any host(here, 192.168.1.3)

 # snmpwalk -v1 -c myu 192.168.2.101

To get uptime of the host, 192.168.2.101, run the following

# snmpget -v1 -c myu 192.168.2.101  HOST-RESOURCES-MIB::hrSystemUptime.0

HOST-RESOURCES-MIB::hrSystemUptime.0 = Timeticks: (272328) 0:45:23.28

To get the numerical format of HOST-RESOURCES-MIB::hrSystemUptime.0

# snmptranslate -On HOST-RESOURCES-MIB::hrSystemUptime.0

.1.3.6.1.2.1.25.1.1.0

# snmpget -v1 -c myu 192.168.2.101 .1.3.6.1.2.1.25.1.1.0

HOST-RESOURCES-MIB::hrSystemUptime.0 = Timeticks: (59650) 0:09:56.50

To avoid typing "-v1 -c myu" for each command, do the following in the client/agent node(here, 192.168.1.3) :

 Create ~/.snmp/snmp.conf file with the following lines

   

 defVersion    1

 defCommunity  myu

Now run snmpwalk or snmpget command without "-v 1 -c public" from the client node(192.168.1.3), as follows

$ snmpwalk 192.168.2.101

Using snmp v3 for queries

SNMP v3 uses user based security model(usm) to control access to the managed device MIB. A username(securityname) must be provided as part of the SNMP request along with a password associatd with that username. On CentOS, the username and password for a SNMP v3 user is kept in file /var/lib/net-snmp/snmpd.conf. Information stored in this account shall be encrypted so that it is readable only by the snmpd dameon. Passwords can be stored as either SHA or MD5 hashes. The password supplied must be greater than 8 characters.

SNMP v3 allows one to choose any combination of hashed authentication(auth) or encrypted data privacy(priv)

1. If just authentication alone, then auth alone can be chosen
2. if privacy alone needed, then choose priv
3. If both auth and privacy are needed choose authpriv 

In the machine where snmpd server is running(say, 192.168.2.101), create a SNMP user, say named "snmpusr" with password and shared secret as "snmppasswd", using command net-snmp-create-v3-user. 

We use md5 hash for the password and DES for data encryption.

snmpd service must be stopped before creating the user.

1. service snmpd stop
2. net-snmp-create-v3-user -A snmppasswd -X snmppasswd -a MD5 -x DES snmpusr
3. adding the following line to /var/lib/net-snmp/snmpd.conf:

• createUser snmpusr MD5 "snmppasswd" DES snmppasswd

adding the following line to /etc/snmp/snmpd.conf:

   rwuser snmpusr

   4. service snmpd start

Now let us try doing a snmpwalk for SNMP v3 users from the client machine(client can run in the same machine as server too)

# snmpwalk -v 3 -u snmpusr -l authpriv -a MD5 -x DES -A snmppasswd -X snmppasswd 192.168.2.101

In order to make the above command simple, update ~/.snmp/snmp.conf in client as follows

defVersion  3

defSecurityName  snmpusr

defSecurityLevel authpriv

defauthpassphrase snmppasswd

defauthpasswd  snmppasswd

defauthtype  MD5

defprivtype  DES

MIB paths of interest for query

CPU  Statistics

        Load

               1 minute Load: .1.3.6.1.4.1.2021.10.1.3.1

               5 minute Load: .1.3.6.1.4.1.2021.10.1.3.2

               15 minute Load: .1.3.6.1.4.1.2021.10.1.3.3

       CPU

               percentage of user CPU time:    .1.3.6.1.4.1.2021.11.9.0

               raw user cpu time:                  .1.3.6.1.4.1.2021.11.50.0

               percentages of system CPU time: .1.3.6.1.4.1.2021.11.10.0

               raw system cpu time:              .1.3.6.1.4.1.2021.11.52.0

               percentages of idle CPU time:   .1.3.6.1.4.1.2021.11.11.0

               raw idle cpu time:                   .1.3.6.1.4.1.2021.11.53.0

               raw nice cpu time:                  .1.3.6.1.4.1.2021.11.51.0

Memory Statistics

               Total Swap Size:                .1.3.6.1.4.1.2021.4.3.0

               Available Swap Space:         .1.3.6.1.4.1.2021.4.4.0

               Total RAM in machine:          .1.3.6.1.4.1.2021.4.5.0

               Total RAM used:                  .1.3.6.1.4.1.2021.4.6.0

               Total RAM Free:                   .1.3.6.1.4.1.2021.4.11.0

               Total RAM Shared:                .1.3.6.1.4.1.2021.4.13.0

               Total RAM Buffered:              .1.3.6.1.4.1.2021.4.14.0

               Total Cached Memory:           .1.3.6.1.4.1.2021.4.15.0

Disk Statistics

       The snmpd.conf needs to be edited. Add the following (assuming a machine with a single '/' partition):

                               disk    /       100000  (or)

                               includeAllDisks 10% for all partitions and disks

       The OIDs are as follows

               Path where the disk is mounted:                 .1.3.6.1.4.1.2021.9.1.2.1

               Path of the device for the partition:            .1.3.6.1.4.1.2021.9.1.3.1

               Total size of the disk/partion (kBytes):        .1.3.6.1.4.1.2021.9.1.6.1

               Available space on the disk:                      .1.3.6.1.4.1.2021.9.1.7.1

               Used space on the disk:                           .1.3.6.1.4.1.2021.9.1.8.1

               Percentage of space used on disk:             .1.3.6.1.4.1.2021.9.1.9.1

               Percentage of inodes used on disk:            .1.3.6.1.4.1.2021.9.1.10.1

OpenVZ HowTo

For installing openvz , first an OS need to be installed. So CentOS is first installed on bare machine, which is followed by Openvz installation

OpenVZ setup involves the basic two steps

1. Installation of Openvz kernel and booting into the kernel
2. Downloading of precreated OS template distribution of your choice(CentOS, Debian, Ubuntu etc) and installing them.

OpenVZ kernel installation

Get the OpenVZ repository. The repository has the openvz kernels

# cd /etc/yum.repos.d/

# wget http://download.openvz.org/openvz.repo

# rpm --import http://download.openvz.org/RPM-GPG-Key-OpenVZ

# yum update

# yum search vzkernel

======N/S Matched: vzkernel =============

vzkernel.i686 : The Linux kernel

vzkernel.x86_64 : The Linux kernel

vzkernel-devel.i686 : Development package for building kernel modules to match

                    : the kernel

vzkernel-devel.x86_64 : Development package for building kernel modules to match

                      : the kernel

vzkernel-firmware.noarch : Firmware files used by the Linux kernel

vzkernel-headers.i686 : Header files for the Linux kernel for use by glibc

vzkernel-headers.x86_64 : Header files for the Linux kernel for use by glibc

If the machine of x86_64 architecture and the base OS(CentOS) installed is 64-bit, install vzkernel.x86_64

# yum install vzkernel.x86_64 vzkernel-devel.x86_64 vzkernel-headers.x86_64

Check  /boot/grub/menu.lst. It must have the entry for the new kernel

title OpenVZ (2.6.32-042stab057.1)

        root (hd0,0)

        kernel /vmlinuz-2.6.32-042stab057.1 ro root=UUID=fffff7aa-57b8-40aa-baa4-588c4eff7651 rd_NO_LUKS rd_NO_LVM LANG=en_US.UTF-8 rd_NO_MD quiet SYSFONT=latarcyrheb-sun16 rhgb crashkernel=auto  KEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM

        initrd /initramfs-2.6.32-042stab057.1.img

# yum install vzctl vzquota

Ensure /etc/sysctl.conf has the following entries

net.ipv4.ip_forward=1

net.ipv4.conf.all.rp_filter=1

net.ipv4.icmp_echo_ignore_broadcasts=1 

net.ipv4.conf.default.forwarding=1

net.ipv4.conf.default.proxy_arp = 0

kernel.sysrq = 1

net.ipv4.conf.default.send_redirects = 1

net.ipv4.conf.all.send_redirects = 0

net.ipv4.conf.eth0.proxy_arp=1

Update the new kernel settings

# sysctl -p

Disable SELINUX . In the file, /etc/selinux/config, set

SELINUX=disabled

Reboot the machine

# shutdown -r now

In the grub menu, a new kernel will apppear(2.6.32-042stab057.1, in my case). Boot this kernel

Once booted, Check that a new network interface, venet0, exists

# ifconfig venet0

venet0    Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00

          inet6 addr: fe80::1/128 Scope:Link

          UP BROADCAST POINTOPOINT RUNNING NOARP  MTU:1500  Metric:1

          RX packets:374 errors:0 dropped:0 overruns:0 frame:0

          TX packets:454 errors:0 dropped:6 overruns:0 carrier:0

          collisions:0 txqueuelen:0

          RX bytes:37637 (36.7 KiB)  TX bytes:39793 (38.8 KiB)

Also, check if the vz service is running

# /etc/init.d/vz status

OpenVZ is running...

Installation of VPS with OS of our choice

For creating virtual machines(VPS) with OpenVZ, we need to have templates for the distribution (centos, debian, ubuntu) that we want to install

The precreated distribution templates can be downloaded from  http://wiki.openvz.org/Download/template/precreated

Download the precreated template distributions of your choice and store it under /vz/template/cache

# wget http://download.openvz.org/template/precreated/debian-6.0-x86_64.tar.gz -P /vz/template/cache

# wget http://download.openvz.org/template/precreated/centos-6-x86_64.tar.gz -P /vz/template/cache

I have downloaded the precreated template distributions of centos 64 bit and debian 64 bit.

To set up a VPS from the centos template, run the following command

# vzctl create 101 --ostemplate  centos-6-x86

Creating container private area (centos-6-x86)

Performing postcreate actions

CT configuration saved to /etc/vz/conf/101.conf

Container private area was created

Here, 101 is the uid of the newly created VPS.

To set a hostname and IP address for the vm, run:

# vzctl set 101 --hostname centos32 --save

# vzctl set 101 --ipadd 192.168.2.101 --save

The ipaddress 192.168.2.101 is assigned to venet0:0

The above steps can be done in a single step

# vzctl create 101 --ostemplate  centos-6-x86 --ipadd 192.168.2.101 --hostname centos32 

To get a list of all vms and their statuses, run

# vzlist -a

After the creation, initialize the created VPS via:

# vzctl start 101

Starting container ...

Container is mounted

Adding IP address(es): 192.168.2.101

Setting CPU units: 1000

Container start in progress...

If you want to have the vm started at boot, run

# vzctl set 101 --onboot yes --save

You can now enter into the VPS by simply SSH'ing into it or via the following command:

#vzctl enter 101

To set a root password for the vm, execute

#vzctl exec 101 passwd

Suppose we want to add an additional ip address, this

# vzctl set 101 --save --ipadd 192.168.2.102

The ipaddress 10.10.37.102 is assigned to venet0:1

Suppose we want to remove an ip address from the VPS

# vzctl set 101 --save --ipdel 192.168.2.102

To leave the vm's console, type

# exit

To stop a vm, run

# vzctl stop 101

To restart a vm, run

# vzctl restart 101

To delete a vm from the hard drive (it must be stopped before you can do this), run

# vzctl destroy 101

To find out about the resources allocated to a vm, run

# vzctl exec 101 cat /proc/user_beancounters

Version: 2.5

       uid  resource                     held              maxheld              barrier                limit              failcnt

      101:  kmemsize                  3409952              4366336  9223372036854775807  9223372036854775807                    0

            lockedpages                     0                    0  9223372036854775807  9223372036854775807                    0

            privvmpages                 10732                11784  9223372036854775807  9223372036854775807                    0

            shmpages                      129                  129  9223372036854775807  9223372036854775807                    0

            dummy                           0                    0                    0                    0                    0

            numproc                        17                   36  9223372036854775807  9223372036854775807                    0

            physpages                    5378                 6261                    0                65536                    0

            vmguarpages                     0                    0  9223372036854775807  9223372036854775807                    0

            oomguarpages                 1566                 1566  9223372036854775807  9223372036854775807                    0

            numtcpsock                      4                    4  9223372036854775807  9223372036854775807                    0

            numflock                        4                    5  9223372036854775807  9223372036854775807                    0

            numpty                          0                    1  9223372036854775807  9223372036854775807                    0

            numsiginfo                      0                   27  9223372036854775807  9223372036854775807                    0

            tcpsndbuf                   69760                69760  9223372036854775807  9223372036854775807                    0

            tcprcvbuf                   65536                65536  9223372036854775807  9223372036854775807                    0

            othersockbuf                 4624                59320  9223372036854775807  9223372036854775807                    0

            dgramrcvbuf                     0                 4360  9223372036854775807  9223372036854775807                    0

            numothersock                   30                   48  9223372036854775807  9223372036854775807                    0

            dcachesize                1341986              1363836  9223372036854775807  9223372036854775807                    0

            numfile                       319                  390  9223372036854775807  9223372036854775807                    0

            dummy                           0                    0                    0                    0                    0

            dummy                           0                    0                    0                    0                    0

            dummy                           0                    0                    0                    0                    0

            numiptent                      20                   20  9223372036854775807  9223372036854775807                    0

The failcnt column is very important, it should contain only zeros; if it doesn't, this means that the vm needs more resources than are currently allocated to the vm. Open the vm's configuration file in /etc/vz/conf and raise the appropriate resource, then restart the vm.

VPS disk space

By default, each VPS created is allocated 2GB disk space and 200000 inodes

# vzctl exec 101 df -h

Filesystem            Size  Used Avail Use% Mounted on

/dev/simfs            2.0G  570M  1.5G  28% /

none                  128M  4.0K  128M   1% /dev

none                  128M     0  128M   0% /dev/shm

# vzctl exec 101 df -i

Filesystem            Inodes   IUsed   IFree IUse% Mounted on

/dev/simfs            200000   21507  178493   11% /

none                   32768     151   32617    1% /dev

none                   32768       1   32767    1% /dev/shm

To increase the available disk space from the default 2GB to something more useful like 10GB: 

This will not immediately consume 10GB of space by the container, but will allocate a maximum of 10GB of hard drive space to it.

# vzctl set 101 --diskspace 10G:11G --save

CT configuration saved to /etc/vz/conf/101.conf

The above command increases the default 2GB drive space available to a barrier of 10GB and a maximum limit of 11GB. The upper limit allows for some grace; the disk space permitted will be 10GB but if it exceeds it, it won’t be restricted from that resource until the barrier is hit. This gives the container a 1GB “buffer.”

# vzctl exec 101 df -h

Filesystem            Size  Used Avail Use% Mounted on

/dev/simfs             10G  570M  9.5G   6% /

none                  128M  4.0K  128M   1% /dev

none                  128M     0  128M   0% /dev/shm

There are two ways to change settings for containers. 

• The first is using vzctl as above (remember to use the –save option to make the changes persistent). 
• The second is to edit the configuration file for the container. For a container with a CTID of 101, the file would be /etc/sysconfig/vz-scripts/101.conf. This file can be used to change options to the container and can also be used to see what existing configuration settings are.

Connecting VPS to Internet

In the main node(not VPS), on which the VPS is being run, run the follwoing command

# iptables -L

If such an entry is observed

REJECT     all  --  anywhere             anywhere            reject-with icmp-host-prohibited

then add these two rules

iptables -A FORWARD -s xxx.xxx.xxx.xxx/xx -j ACCEPT

iptables -A FORWARD -d xxx.xxx.xxx.xxx/xx -j ACCEPT

NOTE: For example, if VPS IP address range is in 192.168.2.1 ~ 192.168.2.254, xxx.xxx.xxx.xxx/xx will be 192.168.2.0/24. So we shall add

# iptables -A FORWARD -s 192.168.2.0/24 -j ACCEPT

# iptables -A FORWARD -d 192.168.2.0/24 -j ACCEPT

Make sure that these two rules are placed above the rule 

"REJECT     all  --  anywhere             anywhere            reject-with icmp-host-prohibited"

Edit /etc/sysconfig/iptables and restart the iptables service (service iptables restart). Now iptables will be listed as follows

#iptables -L

...

ACCEPT     all  --  192.168.2.0/24       anywhere

ACCEPT     all  --  anywhere             192.168.2.0/24

REJECT     all  --  anywhere             anywhere            reject-with icmp-host-prohibited

Add a POSTROUTING chain and a MASQUERADE target

# iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE

Now set the nameserver of main node as the nameserver for the VPS too

# vzctl set 101 --nameserver 192.168.1.1 --save

CT configuration saved to /etc/vz/conf/101.conf

Enable ssh server in MacBook

To log in to your macbook through ssh, ssh server need to be enabled in macbook.
ssh server can be enabled in macbook as follows

1) Go to System Preferences ----->  Internet & Wireless -----> Sharing
2) Check Remote Login box
3) ssh server is now enabled in your macbook. You can even set access restrictions based on users.
4) Click the lock at the bottom to prevent further changes

Creating LVM in single disk in CentOS

Logical volume management is a widely-used technique for deploying logical storage rather than physical storage. With LVM, "logical" partitions can span across physical hard drives and can be resized (unlike traditional ext4/ext3 "raw" partitions).

Say, I have a 160GB hard disk and want to create LVM in this disk. Here is the way to go

LVM (Logical Volume Management) makes use of the device-mapper feature of the Linux kernel to provide a system of partitions that is independent of the underlying disk's layout.

So first load the device mapper module.

# modprobe dm-mod
# lsmod | grep dm_mod


Creating logical volume partitions involves 3 steps

1. Creating Physical Volumes
2. Forming Volume Group using the Physical Volumes
3. Creating Logical Volume partitions on the Volume Group

Step 1 : Create a physical volume


Firstly, we need to create disk partitions of type LVM.  Say, now I want to create 3 disk partitions of type LVM.  I shall be using these 3 partitions like separate disks, for creating logical partitions on them. Since I have 125GB out of 160GB, free in my hard disk(not allocated to any partition earlier and no file system written on it), I use that space to create 3 partitions of size around 41GB each. fdisk comes to the aid of it and here is the way. Basically, fdisk creates raw partitions

[root@dhcppc1 ~]# fdisk /dev/sda

WARNING: DOS-compatible mode is deprecated. It's strongly recommended to
         switch off the mode (command 'c') and change display units to
         sectors (command 'u').


Command (m for help): p

Disk /dev/sda: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000e6ea7


   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          39      307200   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2              39        2589    20480000   83  Linux
/dev/sda3            2589        3226     5120000   82  Linux swap / Solaris
/dev/sda4            3226       19457   130380128+   5  Extended


Creating new partitions now 

Command (m for help): n
First cylinder (3226-19457, default 3226):
Using default value 3226
Last cylinder, +cylinders or +size{K,M,G} (3226-19457, default 19457): +41G


Command (m for help): n
First cylinder (8579-19457, default 8579):
Using default value 8579
Last cylinder, +cylinders or +size{K,M,G} (8579-19457, default 19457): +41G


Command (m for help): n
First cylinder (13932-19457, default 13932):
Using default value 13932
Last cylinder, +cylinders or +size{K,M,G} (13932-19457, default 19457):
Using default value 19457


Command (m for help): p


Disk /dev/sda: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000e6ea7


   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          39      307200   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2              39        2589    20480000   83  Linux
/dev/sda3            2589        3226     5120000   82  Linux swap / Solaris
/dev/sda4            3226       19457   130380128+   5  Extended
/dev/sda5            3226        8578    42994529+  83  Linux
/dev/sda6            8579       13931    42997941   83  Linux
/dev/sda7           13932       19457    44387563+  83  Linux
.
The partitions 5(/dev/sda5), 6(/dev/sda6), 7(/dev/sda7) are the newly created raw partitions
Need to convert the newly created partitions to lvm type

Command (m for help): t
Partition number (1-7): 5
Hex code (type L to list codes): 8e
Changed system type of partition 5 to 8e (Linux LVM)


Command (m for help): t
Partition number (1-7): 6
Hex code (type L to list codes): 8e
Changed system type of partition 6 to 8e (Linux LVM)


Command (m for help): t
Partition number (1-7): 7
Hex code (type L to list codes): 8e
Changed system type of partition 7 to 8e (Linux LVM)


Command (m for help): p


Disk /dev/sda: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000e6ea7


   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          39      307200   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2              39        2589    20480000   83  Linux
/dev/sda3            2589        3226     5120000   82  Linux swap / Solaris
/dev/sda4            3226       19457   130380128+   5  Extended
/dev/sda5            3226        8578    42994529+  8e  Linux LVM
/dev/sda6            8579       13931    42997941   8e  Linux LVM
/dev/sda7           13932       19457    44387563+  8e  Linux LVM


Finally press w write table to disk and exit and reboot
Command (m for help): w
The partition table has been altered!


Calling ioctl() to re-read partition table.


WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table. The new table will be used at
the next reboot or after you run partprobe(8) or kpartx(8)
Syncing disks.

Now, reboot the system.

Creating physical volume using the newly created raw partitions

# pvcreate /dev/sda5

# pvcreate /dev/sda6

The pvdisplay command displays all physical volumes on your system.

# pvdisplay 

[root@dhcppc1 ~]# pvdisplay

  "/dev/sda5" is a new physical volume of "41.00 GiB"

  --- NEW Physical volume ---

  PV Name               /dev/sda5

  VG Name

  PV Size               41.00 GiB

  Allocatable           NO

  PE Size               0

  Total PE              0

  Free PE               0

  Allocated PE          0

  PV UUID               V0ObJ7-y6E3-kJrv-Zee2-SSOe-46lB-303xuf

  "/dev/sda6" is a new physical volume of "41.01 GiB"

  --- NEW Physical volume ---

  PV Name               /dev/sda6

  VG Name

  PV Size               41.01 GiB

  Allocatable           NO

  PE Size               0

  Total PE              0

  Free PE               0

  Allocated PE          0

  PV UUID               5cDz8n-C43V-juxj-0DTD-2yMD-u5R0-fI4hVB

Step 2 : Create a Volume Group - VolGroup

Using the two physical volumes created in previous step using pvcreate command, a volume group can be formed. Let us create a volume group named as, VolGroup (choose any name of your choice), for example.

[root@dhcppc1 ~]# vgcreate  VolGroup /dev/sda5 /dev/sda6

  Volume group "VolGroup" successfully created

Use vgdisplay command to display the details about the Volume Group created

[root@dhcppc1 ~]# vgdisplay

  --- Volume group ---

  VG Name               VolGroup

  System ID

  Format                lvm2

  Metadata Areas        2

  Metadata Sequence No  1

  VG Access             read/write

  VG Status             resizable

  MAX LV                0

  Cur LV                0

  Open LV               0

  Max PV                0

  Cur PV                2

  Act PV                2

  VG Size               82.00 GiB

  PE Size               4.00 MiB

  Total PE              20993

  Alloc PE / Size       0 / 0

  Free  PE / Size       20993 / 82.00 GiB

  VG UUID               ZcdhvM-5Q5O-dffd-CA7e-JuQC-mIqM-SffOpx

Additional PVs can be added to this volume group using the vgextend command

# pvcreate /dev/sda7

  Writing physical volume data to disk "/dev/sda7"

  Physical volume "/dev/sda7" successfully created

# vgextend VolGroup /dev/sda7

  Volume group "VolGroup" successfully extended

# vgdisplay

  --- Volume group ---

  VG Name               VolGroup

  System ID

  Format                lvm2

  Metadata Areas        3

  Metadata Sequence No  2

  VG Access             read/write

  VG Status             resizable

  MAX LV                0

  Cur LV                0

  Open LV               0

  Max PV                0

  Cur PV                3

  Act PV                3

  VG Size               124.33 GiB

  PE Size               4.00 MiB

  Total PE              31829

  Alloc PE / Size       0 / 0

  Free  PE / Size       31829 / 124.33 GiB

  VG UUID               ZcdhvM-5Q5O-dffd-CA7e-JuQC-mIqM-SffOpx

The newly added PV(/dev/sda7) can be removed from volume_group_one by the vgreduce command

# vgreduce VolGroup /dev/sda7

  Removed "/dev/sda7" from volume group "VolGroup"

# vgdisplay VolGroup

  --- Volume group ---

  VG Name               VolGroup

  System ID

  Format                lvm2

  Metadata Areas        2

  Metadata Sequence No  3

  VG Access             read/write

  VG Status             resizable

  MAX LV                0

  Cur LV                0

  Open LV               0

  Max PV                0

  Cur PV                2

  Act PV                2

  VG Size               82.00 GiB

  PE Size               4.00 MiB

  Total PE              20993

  Alloc PE / Size       0 / 0

  Free  PE / Size       20993 / 82.00 GiB

  VG UUID               ZcdhvM-5Q5O-dffd-CA7e-JuQC-mIqM-SffOpx

Adding the Physical Volume(/dev/sda7) Back

[root@dhcppc1 ~]# vgextend VolGroup /dev/sda7

  Volume group "VolGroup" successfully extended

[root@dhcppc1 ~]# vgdisplay VolGroup

  --- Volume group ---

  VG Name               VolGroup

  System ID

  Format                lvm2

  Metadata Areas        3

  Metadata Sequence No  4

  VG Access             read/write

  VG Status             resizable

  MAX LV                0

  Cur LV                0

  Open LV               0

  Max PV                0

  Cur PV                3

  Act PV                3

  VG Size               124.33 GiB

  PE Size               4.00 MiB

  Total PE              31829

  Alloc PE / Size       0 / 0

  Free  PE / Size       31829 / 124.33 GiB

  VG UUID               ZcdhvM-5Q5O-dffd-CA7e-JuQC-mIqM-SffOpx

Step 3 : Creating Logical Volume(LV) partitions


On the Volume Group named VolGroup, now I want to create three logical partitions for home, music and opt. I create a

• 20GB linear LV named logical_volume_home
• 20GB linear LV named logical_volume_music and 
• 5GB linear LV named logical_volume_opt 

from  volume group VolGroup using the lvcreate command as follows:

[root@dhcppc1 ~]# lvcreate -L20GB -n logical_volume_home VolGroup
  Logical volume "logical_volume_home" created
[root@dhcppc1 ~]# lvcreate -L5GB -n logical_volume_opt VolGroup
  Logical volume "logical_volume_opt" created
[root@dhcppc1 ~]# lvcreate -L20GB -n logical_volume_music VolGroup
  Logical volume "logical_volume_music" created

Display status of Logical Volumes

[root@dhcppc1 ~]# lvdisplay
  --- Logical volume ---
  LV Name                /dev/VolGroup/logical_volume_home
  VG Name                VolGroup
  LV UUID                mK0iA2-bYwU-iRFX-bFAN-Ghcg-Q0DO-f1HGVe
  LV Write Access        read/write
  LV Status              available
  # open                 0
  LV Size                20.00 GiB
  Current LE             5120
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:0


  --- Logical volume ---
  LV Name                /dev/VolGroup/logical_volume_opt
  VG Name                VolGroup
  LV UUID                x9aPWe-yGEk-WybC-hJAE-ikKI-ftuc-e3pQRJ
  LV Write Access        read/write
  LV Status              available
  # open                 0
  LV Size                5.00 GiB
  Current LE             1280
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:1


  --- Logical volume ---
  LV Name                /dev/VolGroup/logical_volume_music
  VG Name                VolGroup
  LV UUID                1meVhn-aa8m-RIBH-pWWk-QlXn-Thgl-atXFkN
  LV Write Access        read/write
  LV Status              available
  # open                 0
  LV Size                20.00 GiB
  Current LE             5120
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:2

Output a report of Logical Volumes

[root@dhcppc1 ~]# lvs
  LV                   VG       Attr   LSize  Origin Snap%  Move Log Copy%  Convert
  logical_volume_home  VolGroup -wi-a- 20.00g
  logical_volume_music VolGroup -wi-a- 20.00g
  logical_volume_opt   VolGroup -wi-a-  5.00g

Create File system on logical volumes

mkfs.ext4 -m 0 /dev/VolGroup/logical_volume_vz
mkfs.ext4 -m 0 /dev/VolGroup/logical_volume_opt
mkfs.ext4 -m 0 /dev/VolGroup/logical_volume_music

the -m option specifies the percentage reserved for the super-user, set this to 0 if you wish not to waste any space, the default is 5%.

Edit /etc/fstab for mounting

Add an entry for your newly created logical volume into /etc/fstab

/dev/VolGroup/logical_volume_vz         /vz           ext4     defaults      0 2
/dev/VolGroup/logical_volume_music   /music       ext4     defaults      0 2
/dev/VolGroup/logical_volume_opt       /opt           ext4     defaults      0 2

Mount the partitions without rebooting


mkdir /vz /music /opt    (Creating mount points)
mount -a


Displaying the newly mounted partitions

mount
df -h

Extending a logical volume partition

Say now we want to extend the /vz (/dev/VolGroup/logical_volume_vz) partition size by 5GB.
A LV can be extended by using the lvextend command. You can specify either an absolute size for the extended LV or how much additional storage you want to add to the LVM. For example:

# lvextend -L12G /dev/VolGroup/logical_volume_vz

will extend LV /dev/VolGroup/logical_volume_vz to 12 GB, while

# lvextend -L+5G /dev/VolGroup/logical_volume_vz (This is what Iam going to do now)
 Extending logical volume logical_volume_vz to 25.00 GiB
  Logical volume logical_volume_vz successfully resized

will extend LV /dev/VolGroup/logical_volume_vz by an additional 5 GB. Once a logical volume has been extended, the underlying file system has to be expanded to exploit the additional storage now available on the LV. To resize ext4fs, the following commands need to be run

umount /vz
e2fsck -f /dev/VolGroup/logical_volume_vz
resize2fs /dev/VolGroup/logical_volume_vz

This will extend the ext4 file system to completely fill the LV, /dev/VolGroup/logical_volume_vz, on which it resides.


Remounting the newly created partition
# mount -a

Removing a logical volume from Volume Group

lvdisplay

umount /dev/VolGroup/logical_volume_opt

lvremove /dev/VolGroup/logical_volume_opt