Linux/UNIX Commands For DBAs

Here we learn some useful Linux commands for dba.

Read: How to add SWAP Space in Linux

Useful Linux commands for an Oracle DBA

1. PWD: show the present working directory.

$pwd
/home/oracle

2. ls: list all files and directories from a given location, if the location is not given it shows the list from the current directory.

$ls
$ls /u01
$ls -l (list file details)
$ls -a (show hidden files)

3. cd: change directory or switch directory.

$cd /u02

4. touch: This is used to create an empty file with default permissions.

$touch ocp.log

5. rm: is used to remove files and directories from the location.

$rm ocp.log
or
$rm -r directory_name (remove directory with files)

6. mv: move the file from one location to another location or rename the file or directory.

$mv ocp.log /u02/ocp.log (move file in another location)
$mv ocp.log ocptech.log (rename file)

7. cp: make a copy of an existing file using the cp command.

$cp (from) (to)
$cp ocp.log /u02/ocp.log
$cp *.log /u02

8. mkdir: command used to create a new directory.

$mkdir data
or
$mkdir /u01/data

9. rmdir: used to remove directory.

$rmdir data

10. find: is used to find the location of any file.

$find / -name ocp.log
or
$find / -print |grep -i ocp.log

"/" represent the starting directory path.

11. which: find executable file path which you are using

$whcih sqlplus

Basic Linux Commands for DBAs

12. chmod: is used to change the file permissions.

$chmod 777 *.log

Permission info

7 (u+rwx) 7 (g+rwx) 7 (o+rwx) read + write + execute
6 (u+rw) 6 (g+rw) 6 (o+rw) read + write
5 (u+rx) 5 (g+rx) 5 (o+rx) read + execute
4 (u+r) 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

u for the user, g for group & o for others.

You can use characters also instead of number values during granting the permissions.

$chmod o+rwx *.log
$chmod g+r *.log
$chmod -Rx *.log

13. chown: is used to set the ownership.

$chown -R oinstall.dba *
or
chown -R oinstall.dba /u01  (-R for recursive any sub-directory)

14. useradd: used to add a new user at OS level.

$useradd -G oinstall -g dba -d /usr/users/username -m -s /bin/ksh username
or
$useradd oracle

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.

15. usermod: is used to modify existing user settings.

$usermod -s /bin/csh username

16. userdel: delete exiting user from OS level.

$userdel -r my_user

Here "-r" is used to remove the default directory.

17. passwd: is used to set or reset the password for OS users.

$passwd oracle

18. who: show the list of all OS users' connections.

$who
$who | head -5
$who | tail -5
$who | grep -i ora
$who | wc -l

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.

19. ps: show the current process information

$ps
$ps -ef | grep	pmon
$ps -ef | grep -i ora
$ps -ef | grep -i ora | grep -v grep
$ps -ef | grep -i [o]ra

20. kill: used to kill the running process

$kill 231254
or
$kill -9 231254

DBA Unix Commands

21. uname & hostname: get information about the host

$Linux
$ uname -a
$ hostname
$ hostname -i

22. Compress tools in Linux:

These all are the tools available in Linux tar, star, gzip, bzip2, zip, cpio. These tools are used to compress the files, which is consumed a high amount of space on the filesystem. The gzip command compresses the original file and returns it with the .gz extension.

$gzip file_name
$gunzip file_name.gz

The compress command is also used to compress the original file with the ".Z" extension.

$compress file_name
$uncompress file_name

23. vmstat: used to check OS performance.

$ 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 1461956 126328 1951188    0    0    12     7   23   39  0  0 99  0  0
 0  0      0 1461956 126328 1951216    0    0     0    24   47   71  0  0 100  0  0
 0  0      0 1461848 126336 1951216    0    0     0    10   39   65  0  0 100  0  0

24. free: shows the current usage of memory

$ free
             total       used       free     shared    buffers     cached
Mem:       3925088    2465844    1459244          0     126408    1951572
-/+ buffers/cache:     387864    3537224
Swap:      4194296          0    4194296

25. iostat: Report OS i/o stats.

$ iostat
Linux 2.6.32-220.el6.x86_64 (rhel6.localdomain)         09/22/2021      _x86_64_        (2 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           0.12    0.00    0.20    0.18    0.00   99.50

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda               1.68        42.10        23.96    1644442     935896

26. sar: monitor the CPU, memory, disk, and network information using sar command.

sar syntax:

sar [options] [interval [count]]

Available options for sar.

CPU:
Basic CPU: sar [-u] [interval [count]]
Load Average: sar -q [interval [count]]

Memory:
Kernel Paging: sar -B [interval [count]]
Unused Memory: sar -r [interval [count]]
Swap Space: sar -S [interval [count]]

Disk:
Average Disk I/O: sar -b [interval [count]]
Disk I/O: sar -dp [interval [count]]

Network:
Network: sar -n DEV [interval [count]]
Network Errors: sar -n EDEV [interval [count]]

Example: Monitor the CPU usage

$ sar -u 1 5
Linux 2.6.32-220.el6.x86_64 (rhel6.localdomain)         09/22/2021      _x86_64_        (2 CPU)

02:00:00 PM     CPU     %user     %nice   %system   %iowait    %steal     %idle
02:00:01 PM     all      0.53      0.00      0.00      0.00      0.00     99.47
02:00:02 PM     all      0.00      0.00      1.10      0.00      0.00     98.90
02:00:03 PM     all      0.00      0.00      0.57      0.00      0.00     99.43
02:00:04 PM     all      0.00      0.00      0.00      0.00      0.00    100.00
02:00:05 PM     all      0.00      0.00      0.51      0.00      0.00     99.49
Average:        all      0.11      0.00      0.42      0.00      0.00     99.47

1 = output in every one second
5 = show CPU average after five rows.

27. mpstat: show stats of processor

$ mpstat 5 2
Linux 2.6.32-220.el6.x86_64 (rhel6.localdomain)         09/22/2021      _x86_64_        (2 CPU)

02:04:11 PM  CPU    %usr   %nice    %sys %iowait    %irq   %soft  %steal  %guest   %idle
02:04:16 PM  all    0.00    0.00    0.10    0.00    0.00    0.00    0.00    0.00   99.90
02:04:21 PM  all    0.00    0.00    0.00    0.00    0.00    0.10    0.00    0.00   99.90
Average:     all    0.00    0.00    0.05    0.00    0.00    0.05    0.00    0.00   99.90

28. top: show the top running tasks in OS

29. init: shutdown and reboot the server.

$init 6 (reboot the server)
$init 0 (shutdown the server)

30. passwd: used to change the password.

passwd oracle - The command is executed by the root user, to change the password of the oracle user.

#passwd oracle 

passwd - the command is executed by the user who is already logged in to the server. Who wants to change their own password.

$passwd

31. cat: using the cat command we can open a file on the terminal or find the ORA-ERROR line in the file.

$ cat idea_data.log

SQL*Loader: Release 11.2.0.3.0 - Production on Sat Aug 21 10:28:15 2021

Copyright (c) 1982, 2011, Oracle and/or its affiliates.  All rights reserved.

SQL*Loader-128: unable to begin a session
ORA-01017: invalid username/password; logon denied

Or you can find the ORA - Error inside the file.

$ cat idea_data.log |grep -i ORA-
ORA-01017: invalid username/password; logon denied

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 gives a word count, but the "-l" flag alters it to give a line count.

32. Remove old files using the find command

Find 10 days old files with extension ".csv"

$find /u01/delhi/*.csv -mtime +10

or

$find /u01/delhi/ -name *.csv -mtime +10

Remove 10 days old files with extension ".csv"

$find /u01/delhi/ -name *.csv -mtime +10 -exec rm -f {} ;
$find /u01/delhi/ -name *.csv -mtime +10 -exec rm -f {} \;
$find /u01/delhi/ -name *.csv -mtime +10 -delete;

Find big-size files using the find command in the current directory.

$find . -type f -print0 | xargs -0 du -h | sort -hr | head -20

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