The gedit Text Editor

Oracle Database Tips by Donald Burleson

The text editor geditis extremely easy to use because it is intuitive. It can be called from a command line as long as the terminal is open in an XWindows environment. To edit a particular file, type the command gedit </path/filename>. Of course, the gedit editor can also be called from the command line without naming a file. If the gedit button has been added to the taskbar as described at the end of chapter two, simply clicking this button will launch the gedit text editor.

So the obvious question is, ?if geditcan be used, why use vi?? The answer is that vi can be launched from and remain within a command line context, important when using telnet or sshto connect remotely. Therefore, it is important to become familiar with vi.

Run Levels

?Run level? is the term used to describe the mode that the operating system is running in at any given time. The list is easy to understand and remember. Fedora boots to run level 5 by default, which means it will boot into a graphical user interface. The following list describes the available run levels:

Run Level Description
        0 Halt - Turn off the computer
        1 Single user mode
        2 Multiuser, without networking
        3 Full multiuser mode, with networking
        4 Unused
        5 X11 - Graphical User Interface
        6 Reboot

The file /etc/inittab sets the run level at boot. The command grep "default:" /etc/inittab will display the line in this file which sets the default run level.

The init command can be used to change the run level, which will require a shutdown or reboot. Use the command init 0 to shutdown a node. Use the command init 6 to reboot. This command must be run as root.

Refer to Appendix E for instructions on changing the default run level to 3 in order to launch different windows managers.

Starting and Stopping Services

Linux runs programs in the background called services or daemons. Use the service command to start or stop a service or to view a list of all the services and their corresponding statuses. Examples of the service command are as follows:

### start the vsftpd service (ftp server daemon):
service vsftpd start

### stop the vsftpd service:
service vsftpd stop

### restart the vsftpd service:
service vsftpd restart

### view a list of services and the status of each one:
service -'status -all

Turning a Service On/Off

When a Linux server boots up, it lists all of the services it is starting (type [alt+d] when the graphical interface appears). Many of those services are unnecessary for this Oracle Project and certainly slow the machine down at least slightly. With all of those services to start, booting up can take an unbearably long time.

Use the chkconfig command to change the operating system configuration so that a given service starts or does not start at boot time. The sendmail service is the best example of a service that does not need to be started at boot time. It can easily take 5 minutes just to start that one service. The following are a number of examples of how to use chkconfig to toggle sendmail to turn on and off:

### list statuses of each service
chkconfig ?list

### list one service
chkconfig -?list sendmail

### configure so that sendmail never starts on boot
chkconfig sendmail off

### configure so that sendmail starts when booting

## to runlevel 3
chkconfig ?-level 3 sendmail on

For this project, the following services can be turned off with chkconfig to speed up the boot process and lighten the load on the system. If you install the author's suggested list instead of ?everything,? then only the sendmail and PCMCIA will be installed.

chkconfig sendmail off      # email subsystem
chkconfig pcmcia off        # support for laptop pcmcia cards
chkconfig hpoj off          # HP printer drivers
chkconfig spamassassin off # spam filter
chkconfig privoxy off       # web proxy server
chkconfig canna off        # Japanese language support
chkconfig FreeWnn off      # Japanese language support

Command Line Basics

The command line or shell prompt used by Linux offers a wide range of commands. Appendix A lists many commands that will be used as you install and administer Oracle on Linux. There are a number of shells available on Linux. The default shell or command line interpreter is BASH. All of the work done in this project is completed in the BASH shell. Changing shells is unnecessary and not recommended for this project.

Variables and Environmental Variables

A number of variables are used by the Bash shell for its configuration. For example the prompt itself is defined by the variable PS1, which by default equals '[\u@\h \W]\$ '. This odd group of symbols is interpreted by the shell which outputs the prompt that is normally seen when a terminal is open. That prompt can be changed. To save space, many of the screen-shots captured for this book use a shorter prompt. This is done by making the variable PS1 equal to '[\u]\$ '.

Figure 3.6 illustrates the difference between a variable and an environmental variable. To begin, the env command returns a list of all environmental variables which is piped into or combined with grep PS1. Nothing is found. Next, the set command, which lists all variables, is piped into grep PS1. This time, PS1 is found. Therefore, PS1 is a variable, but not an environmental variable.

To make PS1 an environmental variable, the export command is used. Next, var1 and var2 are created, but only var2 is exported into the environment. Then an xterm is launched. Xterm is a child process of the gnome-terminal. It inherits only the environmental variables PS1 and var2.

Environmental variables are important to the Oracle Database Administrator. They are used to pass information to the Oracle processes that are launched from the command line.

Learn More about PC RAC: