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UNIX Commands For DBAs

This article contains a brief list of commands that most UNIX DBAs will need on a regular basis. Over time I've been adding more Linux-related entries.

Related articles.

Basic File Navigation

The "pwd" command displays the current directory.

root> pwd

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

See Linux Files, Directories and 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
644 : final permission

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

root> chmod 777 *.log

Owner      Group      World      Permission
=========  =========  =========  ======================
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

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

See Linux Groups and Users.

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

Process Management

See Linux Process Management (ps, top, renice, kill).

The "ps" command lists current process information.

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

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

# kill 12345
# kill -9 12345

You can kill multiple processes using a single command by combining "kill" with the "ps" and "awk" commands.

# kill -9 `ps -ef | grep ora | awk '{print $2}'`

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 }'

root> hostname

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

Remove Old Files

The find command can be used to supply a list of files to the rm command or the "-delete" command can be used directly.

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

find /backup/logs/daily_backup* -mtime +5 -exec rm -f {} \;

find /backup/logs/daily_backup* -mtime +5 -delete;

File Exists Check

The Bash shell allows you to check for the presence of a file using the "[ -e filepath ]" comparison. In the following script a backup log is renamed if it is present and files older than 30 days are deleted are deleted.

if [ -e /tmp/backup.log ]; then
  DATE_SUFFIX=`date +"%Y"-"%m"-"%d"`
  mv /tmp/backup.log /tmp/backup-$DATE_SUFFIX.log

# Delete old log files.
find /tmp/backup*.log -mtime +30 -delete;

This is one example of a log rotation, where the most current log doesn't include the date in it's name.

Rotate Log Files

See the previous section for another variant on log rotation.

The following script provides an example of how to manage a log rotation using the Bash shell. The log file includes the date in the file name. Files older than 30 days are deleted.

DATE_SUFFIX=`date +"%Y"-"%m"-"%d"`

# Do something that needs logging.
echo "Send this to log" >> $LOG_FILE 2>&1

# Delete old log files.
find /tmp/backup*.log -mtime +30 -delete;

Find Big Files

Find the top 20 biggest files recursively from this directory.

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

Perform Action for Every File in a Directory

The following scripts shows two methods for performing an action for each file in a directory.

for FILE in `ls /tmp/`; do
  # Do something with the file name.
  echo $FILE;

# Or this.

for FILE in $( ls /tmp/ ); do
  echo $FILE

Perform Action for Every Line in a File

The following scripts shows a method for performing an action for each line in a file.

while read LINE; do
  # Do something with the line.
  echo $LINE;
done < /tmp/myfile.txt


An alias is a named shortcut for a longer command using the following format.

alias name='command'

For example, if you require sudo access for a specific command, you might want to include this as an alias so you don't have to remember to type it.

alias myscript='sudo -u oracle /path/to/myscript'

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.

Where available, it is probably better to use the dos2unix and unix2dos commands.

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.

su - oracle <<EOF
rman catalog=rman/rman@w2k1 target=/ cmdfile=my_cmdfile log=my_logfile append 

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

Compress Files

See Linux Archive Tools (tar, star, gzip, bzip2, zip, cpio).

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


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

See the vmstat man page.


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


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
           2.02    0.23    0.51    0.78    0.00   96.46

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
sda               9.23       100.55        62.99    1796672    1125538
dm-0             13.60       100.31        62.99    1792386    1125524
dm-1              0.02         0.08         0.00       1432          0


CPU Usage

See Linux Process Management (ps, top, renice, kill).


On Linux systems sar (System Activity Reporter) is probably one of the simplest and most versatile tools for reporting system utilization including CPU, memory, disk and network activity. It automatically collects system activity statistics when installed using the following command.

# yum install sysstat

The sar command syntax takes the following form.

# sar [options] [interval [count]]

The "options" parameters determine what is reported, which will be discussed later. The "interval" parameter indicates the time interval in seconds between samples. The "count" parameter indicates the number of samples that will be taken before the command ends. If "count" is omitted, the sampling will continue indefinitely. If both "interval" and "count" are omitted, the command will report the values from the 10 minute samples taken since the machine was last restarted.

As seen in the sar man page, there are lots of available options, but some starting points you may find interesting include:

Here is an example of the output from a CPU report.

# sar -u 1 5
Linux 2.6.32-100.0.19.el5 (ol5-112.localdomain) 	06/27/2011

03:10:07 PM     CPU     %user     %nice   %system   %iowait    %steal     %idle
03:10:08 PM     all      0.00      1.01     23.23     75.76      0.00      0.00
03:10:09 PM     all      0.00      1.02     35.71     63.27      0.00      0.00
03:10:10 PM     all      0.98      3.92     35.29     59.80      0.00      0.00
03:10:11 PM     all      0.00      1.03     29.90     69.07      0.00      0.00
03:10:12 PM     all      0.00      2.00     35.00     63.00      0.00      0.00
Average:        all      0.20      1.81     31.85     66.13      0.00      0.00


Reports processor related statistics.

# mpstat 10 2
Linux 2.6.32-100.0.19.el5 (ol5-112.localdomain) 	06/27/2011

01:59:57 PM  CPU   %user   %nice    %sys %iowait    %irq   %soft  %steal   %idle    intr/s
02:00:07 PM  all    1.21    0.00    0.90    0.20    0.00    0.00    0.00   97.69    980.50
02:00:17 PM  all    0.70    0.00    0.40    0.00    0.00    0.10    0.00   98.79    973.77
Average:     all    0.95    0.00    0.65    0.10    0.00    0.05    0.00   98.24    977.14

See the mpstat man page.


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
Swap:  4095992k total,        0k used,  4095992k free,   620116k cached

 2882 oracle    20   0  610m  64m  56m R 24.9  3.2   0:02.20 oracle
 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
 2933 oracle    20   0  605m  34m  30m S  9.8  1.7   0:00.30 oracle
 2888 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
 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 oracle
 2698 oracle    20   0  604m  18m  16m S  0.3  0.9   0:00.17 oracle
 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
    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/0
    4 root      20   0     0    0    0 S  0.0  0.0   0:00.00 ksoftirqd/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, 
FROM   v$session a,
       v$process b
WHERE  a.paddr = b.addr
AND    spid = '&pid';

See the top man page.

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.


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:

Automatic Startup Scripts on Linux

This text has been replaced by a separate article here.


See CRON : Scheduling Tasks on Linux.

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".

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

The entries have the following elements.

field          allowed values
-----          --------------
minute         0-59
hour           0-23
day of month   1-31
month          1-12
day of week    0-7 (both 0 and 7 are Sunday)
user           Valid OS user
command        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

To prevent a new job starting if the last run is still running, consider using flock. The job will only run if a lock can be obtained on the specified lockfile.

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

0 1 * * 0 /usr/bin/flock -n /tmp/weekly_cleanup.lockfile /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.

set -- $(/usr/sbin/cfsmgr -F raw /)
shift 12
[[ "$1" = "$(/bin/hostname -s)" ]] && exit 0
exit 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.

Background Tasks (nohup)

Running a script as a background task allows it to continue running if your terminal connection fails, or if you want to intentionally close the session.

Put your command in a script. Then call the script using nohup, and rediect the output to a logfile.

nohup ./my_long_running_script.sh >> /tmp/my_long_running_script.log >2&1 &

Nohup stands for "no hang up", which keep the process running if you disconnect. The ">>" redirects the output to the log file. The ">2&1" redirects standard error (stderr) to standard out (stdout), so both go to the log file. The "&" releases control back to your terminal. Just using "&" on its own makes the process run in the background, but it will still fail if your terminal session disconnects unless you include nohup.

You check for output from the script by tailing the log file.

tail -f /tmp/my_long_running_script.log

NFS Mount (Sun)

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

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


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.

Create mount point directory.

mkdir /u04/backup

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


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.

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)

See Linux Samba Configuration.

Create a directory to use for the mount point.

# mkdir /host

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

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

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


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.


From the command promot on the PC do the following.

set PATH=PATH;c:cygwinbin;c:cygwinusrX11R6bin
XWin.exe :0 -query <server-name>

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=<client-name>:0.0; export DISPLAY

xauth (Magic Cookie)

Access to X servers can get broken when using su and sudo commands. The xauth command provides a solution to this. The process involves the following stages:

An example of this is shown below.

$ echo $DISPLAY
$ xauth list
ol6.localdomain/unix:12  MIT-MAGIC-COOKIE-1  be64852468ca3c334720b10bb3c4d3cb
$ sudo su oracle
$ xauth add ol6.localdomain/unix:12  MIT-MAGIC-COOKIE-1  be64852468ca3c334720b10bb3c4d3cb
$ export DISPLAY=localhost:12.0

You will now be able to access the X server, just as you could before the user switch.

Useful Profile Settings

See Linux Groups and Users : Important Files.

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.

For more information see:

Hope this helps. Regards Tim...

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