Oracle UNIX Administration Editing and Viewing Files Oracle UNIX/Linux Tips by Burleson Consulting

Viewing and editing files in UNIX

UNIX provides several commands and utility programs for viewing the contents of data files.  These tools are often very foreign and cryptic to the UNIX beginner, but it is critical to the effective management of Oracle that you become comfortable with these powerful tools:

* The vi editor ? pronounced ?vee-eye? ? This is a powerful text-processing program, which, once mastered, is far faster than any text editor known to personal computers.  Inside the vi editor, every key (both uppercase and lowercase) performs an editing function.  For vi for read-only access, files can be accessed using the view command.

* The cat command - The cat (concatenate) command, (like the MS-DOS type command), displays the contents of a file on the screen. For example, entering the command cat food would display the entire food file on your screen.

* The more command ? The more command is used to display a file, one screen at a time.  For example, entering the command more food would list the food file, and you press the spacebar for the next screen of text.

* The head command ? The head command is used to display the first lines of a file.  For example, entering the command head start would display the first three lines of the start file.

* The tail command ? The tail command is used to display the last lines in a file. For example, entering the command tail gating would display the last three lines of the gating file.

Let?s take a quick look at some of these commands

The UNIX cat command

In addition to displaying the contents of UNIX files, the cat command can be used to join file together.  For example, the following command will join together three Oracle trace files and mail then to the DBA:

cat test_ora_1 test_ora_2 test_ora_3 > \
mail ?s ?Daily trace files? don@mydomain.com

The UNIX head and tail commands

The head and tail commands operate in exactly the same fashion in UNIX and they are very useful for the Oracle DBA who wants to view only a portion of a UNIX file.

The most common use of the tail command for the Oracle DBA is monitoring a file as it becomes full.  For example, during an Oracle export, you might want to monitor the new lines being added to the export log file.  For this you can use the tail ?f command to monitor the log:

root> tail ?f exp_customer.log

The tail command is also useful for looking at new lines at the bottom of your Oracle alert log.  For example, the following command will display the last 50 lines of the Oracle alert log:

root> tail -100 $DBA/$ORACLE_SID/bdump/alert_$ORACLE_SID.log|more

Note that output of the tail command is being piped to the more command so that you can view the alert log one page at a time.

Next, let?s explore some important UNIX file management commands. 

File management in UNIX

The Oracle DBA is charged with the total maintenance of all of the files that comprise the Oracle software.  As such, it is imperative that the Oracle DBA fully understand how to manage UNIX files and directories.  This management includes allocating new files, removing old trace and dump files, and managing the growth of the Oracle data files on the server.

The UNIX touch command

The UNIX touch command is used to create an empty file with the proper owners and permissions.  This is the equivalent to the IEFBR14 utility on a mainframe computer, where a file is created without any contents.

root> touch test.exe

root> ls -al test*

-rw-r-----   1 oracle   dba            0 Aug 13 09:43 test.exe

Now let?s take a common Oracle example of the touch command. First, we enter the UNIX pfile alias that we have placed in our .profile file.  This takes us to the location of our Oracle alert log, and the ls ?al command shows us the file:

cheops*testsid-/export/home/oracle
> pfile

cheops*testsid-/u01/app/oracle/admin/testsid/pfile
> ls -al
total 26140
drwxr-xr-x   2 oracle   dba         2048 Jul 18 13:36 .
drwxr-xr-x   9 oracle   dba         2048 Feb 19  2001 ..
-rw-r--r--   1 oracle   dba         2301 Aug 22 13:01 inittestsid.ora
-rw-r--r--   1 oracle   dba         1840 Mar 13 23:00 inittestsid.ora.bkup

Next, we use the mv command to move the alert log to another name.  We do this so future grep commands will not show us old results.

cheops*testsid-/u01/app/oracle/admin/testsid/pfile
> mv inittestsid.ora inittestsid.ora.old

Now, we can re-create an empty alert log file with the touch command.  Of course, this is not required since Oracle will automatically re-allocate the alert log file the first time that he needs to write an alert message:

cheops*testsid-/u01/app/oracle/admin/testsid/pfile
> touch inittestsid.ora

Now, the ls ?al command show us our old and our new alert log files.

cheops*testsid-/u01/app/oracle/admin/testsid/pfile
> ls -al
total 26140
drwxr-xr-x   2 oracle   dba         2048 Sep  4 16:57 .
drwxr-xr-x   9 oracle   dba         2048 Feb 19  2001 ..
-rw-r--r--   1 oracle   dba            0 Sep  4 16:57 inittestsid.ora
-rw-r--r--   1 oracle   dba         1840 Mar 13 23:00 inittestsid.ora.bkup
-rw-r--r--   1 oracle   dba         2301 Aug 22 13:01 inittestsid.ora.old

Controlling UNIX file permission with umask

UNIX has a default permission mask that is used by default by everyone who accesses the Oracle server.  This permission mask is known as umask, and the value of umask controls the default file permissions whenever you create a new UNIX file.

Normally the umask is set system-wide in the /etc/profile file so it applies to all users on the system.  However, often the Oracle DBA will override the default umask by re-setting it in their login file (.profile or .cshrc).

The values for umask are different depending upon whether the file is executable. The umask for the creation of new executable files is calculated base don the value of umask.  In this case, we have set umask=022:

777 Default Permissions

-022 Subtract umask value, for example

-----

755 Permissions of new file

For executable files, the value of umask is computed by taking the difference between 777 (read-write-execute) and the actual value of umask.  The following table illustrates:

Umask value	022	001	143
File permission	755	776	637
Total	777	777	777

In the example below, the default umask of 022 will leave a file with a permission of 755 (owner read-write-execute, all others read-only) as shown below:

root> umask
022

root> touch test.exe

root> ls -al test.exe

-rwxr-xr-x   1 oracle   dba            0 Jan 22 05:36 test.exe

For another example, say we wanted all Oracle owned file to be completely private, such that only oracle could write to them and only members of the DBA group could read them.  We would want permissions of 740.  To do this, we will reset umask to 037:

root>umask 037

root>touch test1.txt

root>ls -al test1*

-rw-r-----   1 oracle   dba            0 Aug 13 09:43 test1.txt

UNIX umask for Oracle text files

The umask for the creation of new text files is calculated as follows:

 666 Default Permissions

-022 Subtract umask mask, for example

-----

 644 Permissions for new file

This example shows us that given the default umask of 666, and subtracting our sample umask value of 022, new text files are created with mode 644, which states that the owner can read and write the file, while members of the group to which the file belongs, and everyone else can only read the new file.

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