DBA related LINUX commands

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

    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+wx)   6 (g+wx)   6 (o+wx)   write + execute

    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

·         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

    root> who | grep -i ora

    root> 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.

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 }'

    oradb01.lynx.co.uk

    root> hostname

    oradb01.lynx.co.uk

·         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

    Alias

·         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.

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 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

    #

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

    -/+ buffers/cache:    2627948    5550936

    Swap:     10289148          0   10289148

    #

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

               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

sar

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]]

                top

Displays top tasks.

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

    -----          --------------

    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