What is Linux? History of Linux

What is Linux?
Red Hat Enterprise Linux (RHEL) is a Linux-based operating system developed by Red Hat and targeted toward the commercialmarket. Red Hat Enterprise Linux is released in server versions for x86, x86-64, Itanium, PowerPC and IBM System z, and desktop versions for x86 and x86-64. All of Red Hat's official support and training and the Red Hat Certification Program center around the Red Hat Enterprise Linux platform. Red Hat Enterprise Linux is often abbreviated to RHEL, although this is not an official designation.
The first version of Red Hat Enterprise Linux to bear the name originally came onto the market as "Red Hat Linux Advanced Server". In 2003 Red Hat rebranded Red Hat Linux Advanced Server to "Red Hat Enterprise Linux AS", and added two more variants, Red Hat Enterprise Linux ES and Red Hat Enterprise Linux WS.
While Red Hat uses strict trademark rules to restrict free re-distribution of their officially supported versions of Red Hat Enterprise Linux, Red Hat freely provides the source code for the distribution's software even for software where this is not mandatory. As a result, several distributors have created re-branded and/or community-supported re-builds of Red Hat Enterprise Linux that can legally be made available, without official support from Red Hat. CentOS and Oracle Linux aim to provide 100% binary compatibility with Red Hat Enterprise Linux.



Linux is, in simplest terms, an operating system. It is the software on a computer that enables applications and the computer operator to access the devices on the computer to perform desired functions. The operating system (OS) relays instructions from an application to, for instance, the computer's processor. The processor performs the instructed task, then sends the results back to the application via the operating system.
Explained in these terms, Linux is very similar to other operating systems, such as Windows and OS X. 
But something sets Linux apart from these operating systems. The Linux operating system represented a $25 billion ecosystem in 2008. Since its inception in 1991, Linux has grown to become a force in computing, powering everything from the New York Stock Exchange to mobile phones to supercomputers to consumer devices. 
As an open operating system, Linux is developed collaboratively, meaning no one company is solely responsible for its development or ongoing support. Companies participating in the Linux economy share research and development costs with their partners and competitors. This spreading of development burden amongst individuals and companies has resulted in a large and efficient ecosystem and unheralded software innovation. 
Over 1,000 developers, from at least 100 different companies, contribute to every kernel release. In the past two years alone, over 3,200 developers from 200 companies have contributed to the kernel--which is just one small piece of a Linux distribution. 
This article will explore the various components of the Linux operating system, how they are created and work together, the communities of Linux, and Linux's incredible impact on the IT ecosystem.

Key features of Linux Operating System:

Following are the key features of the Linux operating system: 

• Multitasking: several programs running at the same time.
• Multiuser: several users on the same machine at the same time (and no two-user licenses!).
• Multiplatform: runs on many different CPU's, not just Intel.
• Multiprocessor/multithreading: it has native kernel support for multiple independent threads of control within a single process memory space.
• It has memory protection between processes, so that one program can't bring the whole system down.
• Demand loads executable: Linux only reads from disk those parts of a program that are actually used.
• Shared copy-on-write pages among executable. This means that multiple process can use the same memory to run in. When one tries to write to that memory, that page (4KB piece of memory) is copied somewhere else. Copy-on-write has two benefits: increasing speed and decreasing memory use.
• Virtual memory using paging (not swapping whole processes) to disk: to a separate partition or a file in the file system, or both, with the possibility of adding more swapping areas during run time (yes, they're still called swapping areas). A total of 16 of these 128 MB (2GB in recent kernels) swapping areas can be used at the same time, for a theoretical total of 2 GB of useable swap space. It is simple to increase this if necessary, by changing a few lines of source code.
• A unified memory pool for user programs and disk cache, so that all free memory can be used for caching, and the cache can be reduced when running large programs.
• All source code is available, including the whole kernel and all drivers, the development tools and all user programs; also, all of it is freely distributable. Plenty of commercial programs are being provided for Linux without source, but everything that has been free, including the entire base operating system, is still free.
• Multiple virtual consoles: several independent login sessions through the console, you switch by pressing a hot-key combination (not dependent on video hardware). These are dynamically allocated; you can use up to 64.
• Supports several common file systems, including minix, Xenix, and all the common system V file systems, and has an advanced file system of its own, which offers file systems of up to 4 TB, and names up to 255 characters long.
• Many networking protocols: the base protocols available in the latest development kernels include TCP, IPv4, IPv6, AX.25, X.25, IPX, DDP (AppleTalk), Netrom, and others. Stable network protocols included in the stable kernels currently include TCP, IPv4, IPX, DDP, and AX.25.

ADVANTAGES AND DISADVANTAGES OF LINUX OPERATING SYSTEM

• Cost – The most obvious advantage of using Linux is the fact that it is free to obtain, while Microsoft products are available for a hefty and sometimes recurring fee. Microsoft licenses typically are only allowed to be installed on a single computer, whereas a Linux distribution can be installed on any number of computers, without paying a single dime.
• Security – In line with the costs, the security aspect of Linux is much stronger than that of Windows. Why should you have to spend extra money for virus protection software? The Linux operating system has been around since the early nineties and has managed to stay secure in the realm of widespread viruses, spyware and adware for all these years. Sure, the argument of the Linux desktop not being as widely used is a factor as to why there are no viruses. My rebuttle is that the Linux operating system is open source and if there were a widespread Linux virus released today, there would be hundreds of patches released tomorrow, either by ordinary people that use the operating system or by the distribution maintainers. We wouldn’t need to wait for a patch from a single company like we do with Windows.
• Choice (Freedom) – The power of choice is a great Linux advantage. With Linux, you have the power to control just about every aspect of the operating system. Two major features you have control of are your desktops look and feel by way of numerous Window Managers, and the kernel. In Windows, your either stuck using the boring default desktop theme, or risking corruption or failure by installing a third-party shell.
• Software - There are so many software choices when it comes to doing any specific task. You could search for a text editor on Freshmeat and yield hundreds, if not thousands of results. My article on 5 Linux text editors you should know about explains how there are so many options just for editing text on the command-line due to the open source nature of Linux. Regular users and programmers contribute applications all the time. Sometimes its a simple modification or feature enhancement of a already existing piece of software, sometimes its a brand new application. In addition, software on Linux tends to be packed with more features and greater usability than software on Windows. Best of all, the vast majority of Linux software is free and open source. Not only are you getting the software for no charge, but you have the option to modify the source codeand add more features if you understand the programming language. What more could you ask for?
• Hardware - Linux is perfect for those old computers with barely any processing power or memory you have sitting in your garage or basement collecting dust. Install Linux and use it as a firewall, a file server, or a backup server. There are endless possibilities. Old 386 or 486 computers with barely any RAM run Linux without any issue. Good luck running Windows on these machines and actually finding a use for them.

Disadvantages of Linux:

• Understanding – Becoming familiar with the Linux operating system requires patience as well as a strong learning curve. You must have the desire to read and figure things out on your own, rather than having everything done for you. Check out the 20 must read howto’s and guides for Linux.
• Compatibility – Because of its free nature, Linux is sometimes behind the curve when it comes to brand new hardware compatibility. Though the kernel contributors and maintainers work hard at keeping the kernel up to date, Linux does not have as much of a corporate backing as alternative operating systems. Sometimes you can find third party applications, sometimes you can’t.
• Alternative Programs – Though Linux developers have done a great job at creating alternatives to popular Windows applications, there are still some applications that exist on Windows that have no equivalent Linux application. Read Alternatives to Windows Applications to find out some of the popular alternatives.

RHEL Commands List:-

Os Version:-

[root@sujeet ~]#   cat /proc/version

[root@sujeet ~]#   cat /etc/redhat-release

RHEL5.4

[root@sujeet ~]#   getconf LONG_BIT
32

[root@sujeet ~]# uname -a

Check Hard-disk & Free Space:-

[root@sujeet ~]# df -h

Filesystem            Size  Used Avail Use% Mounted on

/dev/sda3             222G   99G  113G  47% /

/dev/sda1              99M   12M   83M  12% /boot

tmpfs                 995M   12K  995M   1% /dev/shm

Check Physical Memory :-(swap)

[root@sujeet ~]$ grep MemTotal /proc/meminfo

MemTotal:      3036792 kB

[root@sujeet ~]#   grep SwapTotal /proc/meminfo

SwapTotal:     12192956 kB

  Command to Check the RAM Size 
ORACLE:/home/oracle>free -m

total used free shared buffers cached

Mem: 998 976 22 0 56 540

-/+ buffers/cache: 379 619

Swap: 4502 77 4425

ORACLE:/home/oracle>dmesg | grep RAM

BIOS-provided physical RAM map:

RAMDISK driver initialized: 16 RAM disks of 16384K size 1024 blocksize

ORACLE:/home/oracle>vmstat

procs ----memory----swap--io--system-- ----cpu----

r  b swpd  free     buff   cache   si so bi bo in    cs us sy id wa

0 0 78976 27396 57228 547856 0 0  16 32 575 359 3 0 97 0

ORACLE:/home/oracle>vmstat 2 10

procs -----memory---swap--io----system-- ----cpu----

r b swpd      free buff   cache   si so bi bo in     cs us sy id wa

0 0 78976 30396 58040 543516 0 0 16 32 575 357 3 0 97   0

0 0 78976 30252 58040 543516 0 0 00 1014 218 0 0 100   0

0 0 78976 30252 58040 543516 0 0 02 4 1016 171 0 0 100  0

0 0 78976 30252 58048 543508 0 0 0166 1038 200 0 0 100 0

0 0 78976 30252 58048 543508 0 0 00 1012 184 0 0 99      0

0 0 78976 30252 58048 543508 0 0 024 1014 201 0 0 100 0

0 0 78976 30252 58052 543504 0 0 030 1015 194 0 0 100 0

0 0 78976 30316 58052 543764 0 0 048 1021 181 0 0 100 0

0 0 78976 30252 58060 543756 0 0 032 1015 198 1 0 100 0

0 0 78976 30252 58068 543748 0 0 032 1015 213 0 0 100 0

and top command also shows up free space

2.to check free disk space

ORACLE:/home/oracle>df

Filesystem 1K-blocks Used Available Use% Mounted on

/dev/sda1 20161172 7177644 11959388 38% /

/dev/sda3 50394996 4415128 43419912 10% /d01

/dev/sda2 50394996 1476324 46358716 4% /d02

/dev/sda6 28344028 77888 26826316 1% /d03

none 511344 0 511344 0% /dev/shm

ORACLE:/home/oracle>df -h

Filesystem Size Used Avail Use% Mounted on

/dev/sda1 20G 6.9G 12G 38% /

/dev/sda3 49G 4.3G 42G 10% /d01

/dev/sda2 49G 1.5G 45G 4% /d02

/dev/sda6 28G 77M 26G 1% /d03

none 500M 0 500M 0% /dev/shm

3.uptime - Tell how long the system has been running.

ORACLE:/home/oracle>uptime

18:38:23 up 7:40, 9 users, load average: 0.28, 0.13, 0.10

4.Display Number of CPUs in Linux

To see the number of CPUs on a Linux server, you can cat the /proc/cpuinfo file.

cat /proc/cpuinfo grep processor

ORACLE:/home/oracle>cat /proc/cpuinfo

processor : 0

vendor_id : GenuineIntel

cpu family : 6

model : 7

model name : Intel(R) Core(TM)2 Duo CPU E8200 @ 2.66GHz

stepping : 6

cpu MHz : 2666.830

cache size : 6144 KB

physical id : 0

siblings : 2

core id : 0

cpu cores : 2

fdiv_bug : no

hlt_bug : no

f00f_bug : no

coma_bug : no

fpu : yes

fpu_exception : yes

cpuid level : 10

wp : yes

flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx lm pni monitor ds_cpl est tm2 xtpr

bogomips : 5336.09

which - The "which" command displays the full path of (shell) commands.

which zip
/oracle/db/11.2/bin/zip

cp - The "cp" command is used to copy files and directories

cp [option] SOURCE   DEST

cp file1.txt file2.txt
cp * /archive     (the source = *   ---> from current directory; the destination = /archive )
cp /archive/* .   (the source =/archive/* ;  the destination is = .  ---> the current directory)

mv - The "mv" command is used to move or rename files and directories

mv file1.txt file2.txt
mv * /archive     (the source = *   ---> from current directory; the destination = /archive )
mv /archive/* .   (the source =/archive/* ;  the destination is = .  ---> the current directory)

rm - The "rm" command is used to delete files and directories

ls
Dir1 file1.txt
rm file1.txt
ls
Dir1
rm -R Dir1
ls
 

You can use -R in order to remove a directory.

cd - The "cd" command is used to change directories

/home/oracle/myDir>pwd
/home/oracle/myDir
/home/oracle/myDir>cd ../
/home/oracle>cd myDir
/home/oracle/myDir>
 

mkdir - The "mkdir" command is used to create new directories

mkdir Mydir

find - The "find" command can be used to find the location of specific files

find $ORACLE_HOME -name listener.ora
/oracle/db/11.2/network/admin/samples/listener.ora
 

umask - The "umask" command can be used to set the creation file permisions for an (OS) user

The umask value is subtracted from the default permissions (666) to give the final/ real permission:
 

666 : Default permission
002 : - umask value
664 : final permission

chmod - The "chmod" command can be used to change the file permisions

chmod 777 myfile.txt

Owner      Group      The others    Permission

   7               7               7              read + write + execute
   6               6               6              write + execute
   5               5               5              read + execute
   4               4               4              read only
   2               2               2              write only
   1               1               1              execute only

chown - The "chown" command is used to change the ownership of files

chown oracle:dba tnsnames.ora

chown -R oracle:dba /oracle/base

ps - The "ps" command lists current process information

ps -ef | grep smon

kill - The "kill" command stop a specific OS process

kill -9 3009

3009 is the process ID

scp secure copy

ORACLE:/home/oracle>scp $ORACLE_HOME/dbs/initstby.ora oracle@10.11.12.7:/db/oracle/product/10.2.0/dbs/initstby.ora

oracle@10.11.12.7's password:

initstby.ora 100% 1120 1.1KB/s 00:00

Basic File Navigation

The "pwd" command displays the current directory.

root> pwd

/u01/app/oracle/product/9.2.0.1.0

The "ls" command lists all files and directories in the specified directory. If no location is defined it acts on the current directory.

root> ls

root> ls /u01

root> ls -al

The "-a" flag lists hidden "." files. The "-l" flag lists file details.

The "cd" command is used to change directories.

root> cd /u01/app/oracle

The "touch" command is used to create a new empty file with the default permissions.

root> touch my.log

The "rm" command is used to delete files and directories.

root> rm my.log

root> rm -R /archive

The "-R" flag tells the command to recurse through subdirectories.

The "mv" command is used to move or rename files and directories.

root> mv [from] [to]

root> mv my.log my1.log
root> mv * /archive

.
root> mv /archive/*
 

The "." represents the current directory.

The "cp" command is used to copy files and directories.

root> cp [from] [to]

root> cp my.log my1.log
root> cp * /archive

.
root> cp /archive/*
 

The "mkdir" command is used to create new directories.

root> mkdir archive

The "rmdir" command is used to delete directories.

root> rmdir archive

The "find" command can be used to find the location of specific files.

root> find / -name dbmspool.sql

root> find / -print | grep -i dbmspool.sql

The "/" flag represents the staring directory for the search. Wildcards such as "dbms*" can be used for the filename.

The "which" command can be used to find the location of an executable you are using.

oracle> which sqlplus

The "which" command searches your PATH setting for occurrences of the specified executable.

File Permissions

The "umask" command can be used to read or set default file permissions for the current user.

root> umask 022

The umask value is subtracted from the default permissions (666) to give the final permission.

666 : Default permission
022 : - umask value

on
644 : final permiss
i

The "chmod" command is used to alter file permissions after the file has been created.

root> chmod 777 *.log

wner      Group      World      Permission


O=========  =========  =========  ======================
7 (u+rwx)  7 (g+rwx)  7 (o+rwx)  read + write + execute

)   5 (g+Rx)   5 (o+Rx)   read + execute
4 (u+r)
6 (u+wx)   6 (g+wx)   6 (o+wx)   write + execute
5 (u+R
x    4 (g+r)    4 (o+r)    read only
2 (u+w)    2 (g+w)    2 (o+w)    write only

1 (u+x)    1 (g+x)    1 (o+x)    execute only

Character eqivalents can be used in the chmod command.

root> chmod o+rwx *.log
root> chmod g+r   *.log

root> chmod -Rx   *.log

The "chown" command is used to reset the ownership of files after creation.

root> chown -R oinstall.dba *

The "-R" flag causes the command ro recurse through any subdirectories.

OS Users Management

The "useradd" command is used to add OS users.

root> useradd -G oinstall -g dba -d /usr/users/my_user -m -s /bin/ksh my_user

• The "-G" flag specifies the primary group.
• The "-g" flag specifies the secondary group.
• The "-d" flag specifies the default directory.
• The "-m" flag creates the default directory.
• The "-s" flag specifies the default shell.

The "usermod" command is used to modify the user settings after a user has been created.

root> usermod -s /bin/csh my_user

The "userdel" command is used to delete existing users.

root> userdel -r my_user

The "-r" flag removes the default directory.

The "passwd" command is used to set, or reset, the users login password.

root> passwd my_user

The "who" command can be used to list all users who have OS connections.

root> who

root> who | head -5
root> who | tail -5

ora
root> who | wc -l
root> who | grep -i

 

• The "head -5" command restricts the output to the first 5 lines of the who command.
• The "tail -5" command restricts the output to the last 5 lines of the who command.
• The "grep -i ora" command restricts the output to lines containing "ora".
• The "wc -l" command returns the number of lines from "who", and hence the number of connected users.

Process Management

The "ps" command lists current process information.

root> ps

root> ps -ef | grep -i ora

Specific processes can be killed by specifying the process id in the kill command.

root> kill -9 12345

uname and hostname

The "uname" and "hostname" commands can be used to get information about the host.

root> uname -a

OSF1 oradb01.lynx.co.uk V5.1 2650 alpha
root> uname -a | awk '{ print $2 }'

adb01.lynx.co.uk
oradb01.lynx.co.uk

root> hostname
o

r

Error Lines in Files

You can return the error lines in a file using.

root> cat alert_LIN1.log | grep -i ORA-

The "grep -i ORA-" command limits the output to lines containing "ORA-". The "-i" flag makes the comparison case insensitive. A count of the error lines can be returned using the "wc" command. This normally give a word count, but the "-l" flag alteres it to give a line count.

root> cat alert_LIN1.log | grep -i ORA- | wc -l

File Exists Check

The Korn shell allows you to check for the presence of a file using the "test -s" command. In the following script a backup log is renamed and moved if it is present.

#!/bin/ksh

if test -s /backup/daily_backup.log
then

E_SUFFIX=`date +"%y""%m""%d""%H""%M"`
  mv
DA

T /backup/daily_backup.log /backup/archive/daily_backup$DATE_SUFFIX.log

fi

Remove Old Files

The find command can be used to supply a list of files to the rm command.

find /backup/logs/ -name daily_backup* -mtime +21 -exec rm -f {} ;

Remove DOS CR/LFs (^M)

Remove DOS style CR/LF characters (^M) from UNIX files using.

sed -e 's/^M$//' filename > tempfile

The newly created tempfile should have the ^M character removed.

Run Commands As Oracle User From Root

The following scripts shows how a number of commands can be run as the "oracle" user the "root" user.

#!/bin/ksh

su - oracle <

ORACLE_SID=LIN1; export ORACLE_SID

rman catalog=rman/rman@w2k1 target=/ cmdfile=my_cmdfile log=my_logfile append 

EOF

This is often necessary where CRON jobs are run from the root user rather than the oracle user.

Compress Files

In order to save space on the filesystem you may wish to compress files such as archived redo logs. This can be using either the gzip or the compress commands. The gzip command results in a compressed copy of the original file with a ".gz" extension. The gunzip command reverses this process.

gzip myfile

gunzip myfile.gz

The compress command results in a compressed copy of the original file with a ".Z" extension. The uncompress command reverses this process.

compress myfile

uncompress myfile

General Performance

vmstat

Reports virtual memory statistics.

# vmstat 5 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 995244  24392 799656    0    0  6302   160 1221 1962 10 10 62 18  0
0  0      0 1060608  24372 739080    0    0  1334    63 1018 1571 14 11 66 10  
0
 0  0      0 992376  24400 799784    0    0     1    28  992 1886  3  2 95  0  0


#

free

Reports the current memory usage. The "-/+ buffers/cache:" line represents the true used and free memory, ignoring the Linux file system cache.

# free

             total       used       free     shared    buffers     cached
Mem:       8178884    4669760    3509124          0     324056    1717756

0289148
#
-/+ buffers/cache:    2627948    5550936
Swap:     10289148          0   

1

iostat

Reports I/O statistics.

# iostat

Linux 3.2.10-3.fc16.x86_64 (maggie.localdomain)  03/19/2012  _x86_64_(4 CPU)
avg-cpu:  %user   %nice %system %iowait  %steal   %idle

Device:            tps    kB_read/s    kB_wrtn/s    kB_
2.02    0.23    0.51    0.78    0.00   96.46

read    kB_wrtn

-0             13.60       100.31        62.99    1792386    1125524
d
sda               9.23       100.55        62.99    1796672    1125538
d
mm-1              0.02         0.08         0.00       1432          0



#

CPU Usage

sar

Collect, report, or save system activity information.

# sar -u 10 8

Linux 2.6.32-100.0.19.el5 (ol5-112.localdomain)  06/27/2011

2:01:09 PM       CPU     %user     %nice   %system   %iowait    %steal     %idle

002:01:19 PM       all      1.01      0.00      0.50      0.00      0.00     98.49

2:01:39 PM       all      1.21      0.00      0.60      0.40      0.00     97.79

02:01:29 PM       all      2.72      0.00      2.62      0.10      0.00     94.56

002:01:49 PM       all      1.00      0.00      0.60      0.10      0.00     98.29
02:01:59 PM       all      1.21      0.00      0.70      0.10      0.00     97.99

2:02:29 PM       all      2.92      0.00      2.42      0.10      0.00     94.56

02:02:09 PM       all      1.01      0.00      0.40      0.10      0.00     98.49
02:02:19 PM       all      0.80      0.00      0.50      0.20      0.00     98.49

0Average:          all      1.48      0.00      1.04      0.14      0.00     97.34


#

mpstat

Reports processor related statistics.

# mpstat 10 2

Linux 2.6.32-100.0.19.el5 (ol5-112.localdomain)  06/27/2011

1:59:57 PM  CPU   %user   %nice    %sys %iowait    %irq   %soft  %steal   %idle    intr/s

002:00:07 PM  all    1.21    0.00    0.90    0.20    0.00    0.00    0.00   97.69    980.50

verage:     all    0.95    0.00    0.65    0.10    0.00    0.05    0.00   98.24    977.14

02:00:17 PM  all    0.70    0.00    0.40    0.00    0.00    0.10    0.00   98.79    973.77


A#

top

Displays top tasks.

# top

top - 13:58:17 up 2 min,  1 user,  load average: 2.54, 1.11, 0.41

Tasks: 160 total,   6 running, 154 sleeping,   0 stopped,   0 zombie

Cpu(s): 77.1%us, 22.6%sy,  0.0%ni,  0.0%id,  0.0%wa,  0.3%hi,  0.0%si,  0.0%st
Mem:   2058872k total,   879072k used,  1179800k free,    23580k buffers

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 2
Swap:  4095992k total,        0k used,  4095992k free,   620116k cached

882 oracle    20   0  610m  64m  56m R 24.9  3.2   0:02.20 oracle

 oracle    20   0  605m  34m  30m S  9.8  1.7   0:00.30 oracle
 2
2927 root      20   0 90328 3832 2604 R 24.6  0.2   0:00.89 Xorg
 2931 oracle    20   0  605m  34m  31m R 11.5  1.7   0:00.35 oracle
 293
3888 oracle    20   0  614m  52m  40m S  6.9  2.6   0:00.78 oracle
 2935 oracle    20   0  604m  22m  20m S  6.2  1.1   0:00.19 oracle
 2937 oracle    20   0  604m  19m  17m R  4.6  1.0   0:00.14 oracle


 2698 oracle    20   0  604m  18m  16m S  0.3  0.9   0:00.17 oracl
2688 oracle    -2   0  603m  15m  13m S  4.3  0.8   0:01.08 oracle
 2685 oracle    20   0  603m  15m  13m S  0.7  0.8   0:00.22 oracle
 2939 oracle    20   0  217m 4084 3504 R  0.7  0.2   0:00.02 oracl
ee
 2702 oracle    20   0  609m  22m  14m S  0.3  1.1   0:00.17 oracle
 2704 oracle    20   0  618m  21m  19m S  0.3  1.1   0:00.21 oracle
 2714 oracle    20   0  603m  20m  18m S  0.3  1.0   0:00.18 oracle

0
    4 root      20   0     0    0    0 S  0.0  0.0   0:00.00 ks
1 root      20   0 10364  704  588 S  0.0  0.0   0:00.36 init
    2 root      20   0     0    0    0 S  0.0  0.0   0:00.00 kthreadd
    3 root      RT   0     0    0    0 S  0.0  0.0   0:00.00 migration
/oftirqd/0
    5 root      RT   0     0    0    0 S  0.0  0.0   0:00.00 watchdog/0
    6 root      20   0     0    0    0 S  0.0  0.0   0:00.03 events/0
    7 root      20   0     0    0    0 S  0.0  0.0   0:00.00 cpuset


8 root      20   0     0    0    0 S  0.0  0.0   0:00.00 khelper
    9 root      20   0     0    0    0 S  0.0  0.0   0:00.00 netns


#

The PID column can then be matched with the SPID column on the V$PROCESS view to provide more information on the process.

SELECT a.username, 
a.osuser, 


       spid, 
   
a.program,
     sid, 
       a.serial#

$process b
WHERE  a
FROM   v$session a,
       
v.paddr = b.addr

id';
AND    spid = '&
p

Hide Passwords

You may be required to use passwords in scripts calling Oracle tools, like SQL*Plus, Export/Import and RMAN etc. One method to remove the credentials from the script itself is to create a credentials file to hold them. In this case I'm using "/home/oracle/.scottcred", which contains the following.

scott/tiger

Change the permissions to make sure the file is only visible to the owner.

$ chmod 600 /home/oracle/.scottcred

Now replace references to the credentials with the contents of the file.

$ expdp < /home/oracle/.scottcred schemas=SCOTT directory=DATA_PUMP_DIR dumpfile=SCOTT.dmp logfile=expdpSCOTT.log

Alternatively, consider using one of the following:

• Secure External Password Store
• OS Authentication

Automatic Startup Scripts on Linux

This text has been replaced by a separate article here.

CRON

There are two methods of editing the crontab file. First you can use the "crontab -l > filename" option to list the contents and pipe this to a file. Once you've editied the file you can then apply it using the "crontab filename".

• Login as root
• crontab -l > newcron
• Edit newcron file.
• crontab newcron

Alternatively you can use the "crontab -e" option to edit the crontab file directly.

The entries have the following elements.

field          allowed values
-----          --------------

     0-23
day of mo
minute         0-59
hour     
 nth   1-31
month          1-12

 are Sunday)
user           Valid OS user
co
day of week    0-7 (both 0 and 

7mmand        Valid command or script.

The first 5 fields can be specified using the following rules.

*       - All available values or "first-last".

3-4     - A single range representing each possible from the start to the end of the range inclusive.
1,2,5,6 - A specific list of values.
1-3,5-8 - A specific list of ranges.


0-23/2  - Every other value in the specified range.

The following entry runs a cleanup script a 01:00 each Sunday. Any output or errors from the script are piped to /dev/null to prevent a buildup of mails to root.

0 1 * * 0 /u01/app/oracle/dba/weekly_cleanup > /dev/null 2>&1

Cluster Wide CRON Jobs On Tru64

On clustered systems cron is node-specific. If you need a job to fire once per cluster, rather than once per node you need an alternative approach to the standard cron job. One approach is put forward in the HP best practices document (Using cron in a TruCluster Server Cluster), but in my opinion a more elegant solution is proposed by Jason Orendorf of HP Tru64 Unix Enterprise Team (TruCluster Clustercron).

In his solution Jason creates a file called /bin/cronrun with the following contents.

#!/bin/ksh

set -- $(/usr/sbin/cfsmgr -F raw /)
shift 12

 "$(/bin/hostname -s)" ]] && exit 0
exit 1
[[ "$1" 

=

This script returns TRUE (0) only on the node which is the CFS serving cluster_root.

All cluster wide jobs should have a crontab entry on each node of the cluster like.

5 * * * /bin/cronrun && /usr/local/bin/myjob

Although the cron jobs fire on all nodes, the "/bin/cronrun &&" part of the entry prevents the script from running on all nodes except the current CFS serving cluster_root.

NFS Mount (Sun)

The following deamons must be running for the share to be seen by a PC.

• /usr/lib/nfs/nfsd -a
• /usr/lib/nfs/mountd
• /opt/SUNWpcnfs/sbin/rpc.pcnfsd

To see a list of the nfs mounted drives already present type.

exportfs

First the mount point must be shared so it can be seen by remote machines.

share -F nfs -o ro /cdrom

Next the share can be mounted on a remote machine by root using.

mkdir /cdrom#1

mount -o ro myhost:/cdrom /cdrom#1

NFS Mount (Tru64)

On the server machine, if NFS is not currently setup do the following.

• Application Manager -> System Admin -> Configuration -> NFS
• Select the "Configure system as an NFS server" option.
• Accept all defaults.

Create mount point directory.

mkdir /u04/backup

Append the following entry to the "/etc/exports" file.

/u04/backup

Make sure the correct permissions are granted on the directory.

chmod -R 777 /u04/backup

On the client machine, if NFS is not currently setup do the following.

• Application Manager -> System Admin -> Configuration -> NFS
• Select the "Configure system as an NFS client" option.
• Accept all defaults.

Create mount point directory.

mkdir /backup

Append an following entry to the "/etc/fstab" file.

nfs-server-name:/u04/backup     /backup         nfs rw,bg,intr 0 0

Finally, mount the fileset.

mount /backup

At this point you can start to use the mount point from your client machine. Thanks to Bryan Mills for his help with Tru64.

Samba/CIFS Mount (Linux)

Create a directory to use for the mount point.

# mkdir /host

Add the following line to the "/etc/fstab" file.

//192.168.0.4/public /host   cifs rw,credentials=/root/.smbcred,uid=500,guid=500 0 0

Create a file called "/root/.smbcred" with the following contents.

username=myuser

password=mypassword

Change the permissions on the credentials file.

# chmod 600 /root/.smbcred

Mount the share.

# mount /host

PC XStation Configuration

Download the CygWin setup.exe from http://www.cygwin.com.

Install, making sure to select all the X11R6 (or XFree86 in older versions) optional packages.

If you need root access add the following entry into the /etc/securettys file on each server.

:0

From the command promot on the PC do the following.

set PATH=PATH;c:cygwinbin;c:cygwinusrX11R6bin

XWin.exe :0 -query 

The X environment should start in a new window.

Many Linux distributions do not start XDMCP by default. To allow XDMCP access from Cygwin edit the "/etc/X11/gdm/gdm.conf" file. Under the "[xdmcp]" section set "Enable=true".

If you are starting any X applications during the session you will need to set the DISPLAY environment variable. Remember, you are acting as an XStation, not the server itself, so this variable must be set as follows.

DISPLAY=:0.0; export DISPLAY

Useful Profile Settings

The following ".profile" settings rely on the default shell for the user being set to the Korn shell (/bin/ksh).

The backspace key can be configured by adding the following entry.

stty erase "^H"

The command line history can be accessed using the [Esc][k] by adding the following entry.

set -o vi

Auto completion of paths using a double strike of the [Esc] key can be configured by adding the following entry.

set filec

Useful Files

Here are some files that may be of use.

Path	Contents
/etc/passwd	User settings
/etc/group	Group settings for users.
/etc/hosts	Hostname lookup information.
/etc/system	Kernel parameters for Solaris.
/etc/sysconfigtab	Kernel parameters for Tru64.
/etc/sysctl.conf	Kernel parameters for Linux.

 [root@sujeet ~]#    cal

Display a calendar

 [root@sujeet ~]#    cat

Display the contents of a file (concatenate)

Examples:

Display a file

$ cat myfile.txt

Copy  file command-
[root@sujeet ~]#    cp  

Copy one or more files to another location

[root@sujeet ~]#     fdisk

Partition table manipulator for Linux

 [root@sujeet ~]#     date

Display or change the date.

 [root@sujeet ~]#     hostname

Print or set system name

SYNTAX
hostname [name]

[root@sujeet ~]#     ifconfig

Interface configurator - display your ip address, network interfaces, transferred and received data information, configure a network interface.

25) [root@sujeet ~]# mv

Move or rename files or directories

Selinux status :- 

[root@sonu oracle]# /usr/sbin/sestatus

SELinux status:                 disabled

[root@sonu oracle]# vi /etc/sysconfig/selinux

Create Directory:-
[root@sonu oracle]# mkdir

Search file-
[root@sonu oracle]# ls –lrt


Os Version:-

[root@sujeet ~]#   cat /proc/version

[root@sujeet ~]#   cat /etc/redhat-release

RHEL5.4





 Check OS 32/64 Bits
[root@sujeet ~]#   getconf LONG_BIT

[root@sujeet ~]# uname –a

CPU Information-
 [root@sujeet ~]#  cat /proc/cpuinfo


Process Management

The "ps" command lists current process information.

root # ps

Secure copy one system to other system.


 [root@sujeet ~]#   scp –r   destination_IP: