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LINUX KT for freshers
1) How to see the version of a Oracle Enterprise Linux server
A: cat /etc/*release*
2) How to verify a package installed is correct
A. rpm -V
This will return no value if the package is successfully installed.
3) How to check if the Linux is 32bit of 64bit
A. uname m, this will give as x86_64 on a 64 bit machine and i686
on a 32 bit machine.
Database version:
[prodora@usncx062 etc]$ sqlplus '/ as sysdba'
SQL*Plus: Release 11.2.0.2.0 Production on Wed Jul 6 06:38:52 2011
Copyright (c) 1982, 2010, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.2.0 - 64bit
Production
With the Partitioning, OLAP, Data Mining and Real Application Testingoptions
SYS@prod AS SYSDBA>select * from v$version;
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BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.2.0 - 64bit
Production
PL/SQL Release 11.2.0.2.0 - Production
CORE 11.2.0.2.0 Production
TNS for Linux: Version 11.2.0.2.0 - Production
NLSRTL Version 11.2.0.2.0 - Production
SYS@prod AS SYSDBA>select version from v$instance;
VERSION
11.2.0.2.0
4) How to check the file size in human readable format using ls command
A. If you give ls -lh this will give the file size like in MB,
GB etc, example below[root@usncx058 fs01]# ls -lh redo01a.log
-rw-rw---- 1 perf1ora oinstall 1.1G May 26 03:58 redo01a.log
5) How to check the system uptime
A. To check the system uptime, use the command uptime, example
below
linapp40.diebold.com]:/home/parapus #uptime
05:12:37 up 16 days, 2:23, 5 users, load average: 0.05, 0.19, 0.17
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6) How to see what are the mount points mounted on a server and see
the size of the mount point in human readable format
A. df -h, example below, try using this command on any Linux server
The first line give the details of File system, in our case it gives the
name of the logical volumeThe second line gives the total size of the logical volume
The third line gives the total size utilized
The fourth line gives the available free space
The fifth line give the mount point name.
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7) What is the command to switch a user in Linux
A. su -
8) What is the command to see the server utilization
A. top, example below
top Header Explanation
PID Process ID
USER Owner of process
PR Process priority
NI Nice value
VIRT Virtual memory used by process
RES Non-swapped physical memory used by the process
SHR Shared memory used by the process
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S Status of process
%CPU Percentage of CPU usage
%MEM Percentage of physical memory usage
TIME+ Total CPU time used by process
top is also interactive.
For example, pressing Shift+M sorts the output by memory usage.
Interactive top Commands
top Command Explanation
Shift+M Sort by memory usage
Shift+P Sort by CPU usage
Shift+N Sort by PID
Shift+T Sort by TIME+
k Kill a specific process by PID
u Sort by specific user
spacebar Immediately refresh the output
h Show help
q Quit top
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9) How to check the memory used on the server
A. Use free -m or cat /proc/meminfo to see the memory status on a
Linux server, example below
In this example the total amount of available memory is 32494 MB.
3091 MB are used by processes and 29403 MB are free for other
applications. Do not get confused by the first line which shows that
25898MB are free! If you look at the usage figures you can see that
most of the memory use is for buffers and cache. Linux always tries to
use RAM to speed up disk operations by using available memory forbuffers (file system metadata) and cache (pages with actual contents
of files or block devices). This helps the system to run faster because
disk information is already in memory which saves I/O operations. If
space is needed by programs or applications like Oracle, then Linux
will
free up the buffers and cache to yield memory for the applications. If
your system runs for a while you will usually see a small number under
the field "free" on the first line.
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$ cat /proc/meminfo also gives the details of memory status as below, this
also give the details of HugePages if it is implemented.
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10) Command to check the process status
$ ps aux this give the details of all the process running on the
machine, this sort as per the PID example below
The header explanation is as below
USER username
PID process id
%CPU CPU utilization
%MEM Memory utilization
VSZ Virtual memory usage of entire process = VmLib + VmExe +
VmData + VmStk
RSS Resident set size = the non-swapped physical memory that a
task has used; Resident Set currently in physical memory including
Code, Data, Stack
TTY terminal
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STAT Status
START Date
TIME Time taken for execution of the command
COMMAND command name (only the executable name). Modifications
to the command name will not be shown. A process marked
is partly dead, waiting to be fully destroyed by its parent.
$ ps aux |grep will sort as per username, example below
11) vmstat reports information about processes, memory, paging,
block IO, traps, and cpu activity, example below
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The following values are under the memory header:
Two columns are under the procs header: r and b. The value under the
r column indicates the number of processes waiting for runtime. The
value under the b column tells you the number of processes in
uninterruptible sleep.
swpd Amount of virtual memory used
free Amount of free memory
buff Amount of memory used in buffers
cache Amount of memory used as cache
Under the swap header:
si Amount of memory swapped in from the disk
so Amount of memory swapped to the disk
Under the io header:
bi Number of blocks received from a block device
bo Number of blocks sent to a block device
Under the system header:
in Number of interrupts per second
cs Number of context switches per second
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Under the cpu header:
us Percentage of time the processor(s) spent running non-kernel code
sy Percentage of time the processor(s) spent running kernel code
id Percentage of time spent not running any code
wa Percentage of time spent waiting for I/O
st Percentage of time the processor(s) spent running kernel code
12) Find out who is utilizing or eating the CPUs
$ ps -eo pcpu,pid,user,args | sort -k 1 -r | head -10
13) Find Out The Top 10 Memory Consuming Process
$ ps aux | sort -nr -k 4 | head -10
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free command also give the swap details
16) Network statistics
To see how to network is utilized, use the below command
$ sar -n DEV | more this data is collected from
/var/log/sa/sa file
$ sar -n DEV -f /var/log/sa/sa25 this will show the data from the file
dated 25th of the current month.
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17) To check which file/directory using space more on a mount point,
use the below command on a Linux server
To check this first cd to the mount point for example if you want to
check the size of each folders under /mnt/oraperf1/perf1db
1) $ cd /mnt/oraperf1/perf1db
2) $ du -sh * |sort -n |tail this will check the folder size in Human
readable format and sort it with size
3) In the above example the app folder is utilizing more
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4) Now cd to that app folder and see what is utilized more, in this way
we can identify what is causing the space issue and check how to
clear this.
18) To list open files use lsof, this will be helpful to trouble shoot
space issue. For example if someone move a file which is currently in
use for clearing space, this wont free up space. To check these use
lsof
lsof /mnt/oraperf6 |more
19) To check the number of CPUs on a system
$ cat /proc/cpuinfo
20) To check the print queue, go to the concurrent manger tier and
issue the below command
$ lpstat -t |grep
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If there is any pending queue it will show as above, if there is nothing
pending it will give the status as below.
21) To give a print you can use the below command
$ lp -d
22) To see the reboot history of a system use the below command
$ last reboot
23) To get the details of CPU give the below command
$ grep "model name" /proc/cpuinfo
24) To see the last 10 file and sort with last modified time, use the
below command
$ ls -lrt |tail
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25) To create soft link use the below command
$ ln -s filename symlink
Example below
$ ln -s /mnt/oradevshare/oraperf1/applptmp temp
$ ls -l temp
lrwxrwxrwx 1 perf1ora oinstall 34 May 26 02:29 temp ->
/mnt/oradevshare/oraperf1/applptmp
26) To create hard link use the below command
$ ln filename hardlink
Please find the details of the Hard Links and Symbolic (or Soft) Links
27) To check the IP address of a server, use the below command
$ hostname -i
Hard Links Symbolic (or Soft) Links
Multiple names pointing to same
inode
Additional names pointing to original
name
Increments link count Separate file
All names are equal Additional names can be broken
Data preserved until all names
removed
Data lost if original name removed
Must be on same file system Can span across file systems
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Example below
28) To see the Kernel IP routing table use the below command
$ netstat r
Example below
29) To see the active connection on a server use the below
command
$ netstat -e |more
Example below
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30) Archiving file and compressing files
To archive files we use tar and to compress files we use gzip
Example below
$ tar -cvf abc.tar abcthis will create an archive of the folder abc
$ gzip abc.tar will compress the abc.tar as abc.tar.gz
31) To uncompress the extract files
To uncompress a file which is compressed using gzip, use the
command below
$ gunzip abc.tar.gz this will uncompress as abc.tar
To extract the files of abc.tar, use the command below
$ tar -xvf abc.tar
32) To create a file use vi/vim editors
The vi/vim editor has three modes
1) Command mode
2) Insert mode
3) EX mode
To create a file
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$ vi abc will Open a vi editor window this will open in command
mode
To go to insert mode, press I now you can enter what you want to
the file
To save the file you have to go to EX mode, to go to EX mode you have
to go to :
To save and quit use :wq
To quit without saving use :q!
Check man vi to get more options