System startup files

System startup files

When you log in, the shell defines your user environment after reading the initialization files that you have set up. The characteristics of your user environment are defined by the values given to your environment variables. You maintain this environment until you log out of the system.

The shell uses two types of profile files when you log in to the operating system. It evaluates the commands contained in the files and then executes the commands to set up your system environment. The files have similar functions, except that the /etc/profile file controls profile variables for all users on a system, whereas the .profile file allows you to customize your own environment.

The shell first runs the commands to set up your system environment in the /etc/environment file and then evaluates the commands contained in the /etc/profile file. After these files are run, the system then checks to see if you have a .profile file in your home directory. If the .profilefile exists, the system runs this file. The .profile file will specify if an environment file also exists. If an environment file exists (usually named .env), the system then runs this file and sets up your environment variables.

The /etc/environment, /etc/profile, and .profile files are run once at login time. The .env file, on the other hand, is run every time you open a new shell or a window.

• /etc/environment file
  The first file that the operating system uses at login time is the /etc/environment file. The /etc/environment file contains variables specifying the basic environment for all processes.
• /etc/profile file
  The second file that the operating system uses at login time is the /etc/profile file.
• .profile file
  The .profile file is present in your home ($HOME) directory and lets you customize your individual working environment.
• .env file
  A fourth file that the operating system uses at login time is the .env file, if your .profile contains the following line: export ENV=$HOME/.env

/etc/environment file

The first file that the operating system uses at login time is the /etc/environment file. The /etc/environment file contains variables specifying the basic environment for all processes.

When a new process begins, the exec subroutine makes an array of strings available that have the form Name=Value. This array of strings is called the environment. Each name defined by one of the strings is called an environment variable or shell variable. The exec subroutine allows the entire environment to be set at one time.

When you log in, the system sets environment variables from the /etc/environment file before reading your login profile, named .profile. The following variables make up the basic environment:

HOME	The full path name of the user's login or HOME directory. The login program sets this to the name specified in the /etc/passwd file.
LANG	The locale name currently in effect. The LANG variable is initially set in the /etc/profile file at installation time.
NLSPATH	The full path name for message catalogs.
LOCPATH	The full path name of the location of National Language Support tables.
PATH	The sequence of directories that commands, such as sh, time, nice and nohup, search when looking for a command whose path name is incomplete.
TZ	The time zone information. The TZ environment variable is initially set by the /etc/profile file, the system login profile.

For detailed information about the /etc/environment file, see the AIX 5L™ Version 5.3 Files Reference.

/etc/profile file

The second file that the operating system uses at login time is the /etc/profile file.

The /etc/profile file controls system-wide default variables, such as:

• Export variables
• File creation mask (umask)
• Terminal types
• Mail messages to indicate when new mail has arrived

The system administrator configures the /etc/profile file for all users on the system. Only the system administrator can change this file.

The following example is a typical /etc/profile file:

#Set file creation mask
unmask 022
#Tell me when new mail arrives
MAIL=/usr/mail/$LOGNAME
#Add my /bin directory to the shell search sequence
PATH=/usr/bin:/usr/sbin:/etc::
#Set terminal type
TERM=lft
#Make some environment variables global
export MAIL PATH TERM

For detailed information about the /etc/profile file, see the AIX 5L™ Version 5.3 Files Reference .

.profile file

The .profile file is present in your home ($HOME) directory and lets you customize your individual working environment.

Because the .profile file is hidden, use the ls -a command to list it.

After the login program adds the LOGNAME (login name) and HOME (login directory) variables to the environment, the commands in the$HOME/.profile file are executed if the file is present. The .profile file contains your individual profile that overrides the variables set in the/etc/profile file. The .profile file is often used to set exported environment variables and terminal modes. You can customize your environment by modifying the .profile file. Use the .profile file to control the following defaults:

• Shells to open
• Prompt appearance
• Keyboard sound

The following example is a typical  .profile file:

PATH=/usr/bin:/etc:/home/bin1:/usr/lpp/tps4.0/user::
epath=/home/gsc/e3:
export PATH epath
csh

This example has defined two path variables (PATH and epath), exported them, and opened a C shell (csh).

You can also use the .profile file (or if it is not present, the /etc/profile file) to determine login shell variables. You can also customize other shell environments. For example, use the .cshrc file and .kshrc file to customize a C shell and a Korn shell, respectively, when each type of shell is started.

.env file

A fourth file that the operating system uses at login time is the .env file, if your .profile contains the following line: export ENV=$HOME/.env

The .env file lets you customize your individual working environment variables. Because the .env file is hidden, use the ls -a command to list it. For more information about the ls command, see ls. The .env file contains the individual user environment variables that override the variables set in the/etc/environment file. You can customize your environment variables as desired by modifying your .env file.

The following example is a typical .env file:

export  myid=`id | sed -n -e 's/).*$//' -e 's/^.*(//p'`
#set prompt: login & system name & path 
if [ $myid = root ]
        then    typeset -x PSCH='#:\${PWD}> '
                PS1="#:\${PWD}> "
        else    typeset -x PSCH='>'
                PS1="$LOGNAME@$UNAME:\${PWD}> "
                PS2=">"
                PS3="#?"
fi
export PS1 PS2 PS3
#setup my command aliases
alias   ls="/bin/ls -CF" \
        d="/bin/ls -Fal | pg" \
        rm="/bin/rm -i" \
        up="cd .."

Note: When modifying the  .env file, ensure that newly created environment variables do not conflict with standard variables such as  MAIL,  PS1,  PS2, and  IFS.

From:

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