Run the below command to check what user and group apache is running as, by typing $ ps auwfx | grep apache2 root 28937 0.0 0.1 3004 756 pts/0 S+ 12:35 0:00 | \_ grep apache2 root 25235 0.0 2.5 37744 12992 ? Ss Mar18 0:06 /usr/sbin/apache2 -k start www-data 27102 0.0 1.3 38252 6972 ? S Mar21 0:00 \_ /usr/sbin/apache2 -k start (more…)

Linux variables have the prefix $. Variables that will be useful in shell scripting are listed below. $$ Process ID number of the shell in execution $? Variable indicating Exit status (from the last command that got executed) $* Entire argument string in the command line (excluding script name) $# Number of arguments in the command line (not counting the shell script name) To access arguments passed to a script, following variables are used. $0 Name of the program (with entire path) $1 First argument passed in the command line $2 Second argument passed in the command line $n Nth argument passed in the command line To move or shift to a specified argument in the list of arguments, "shift" command is used. For example, to shift 1 argument just type "shift" or "shift 1" and to shift to the third argument in the list type "shift 2". (more…)

$PATH is the environment variable related to Linux Path settings. To add a directory to the path, type $ export PATH=$PATH:/tmp/myshells The above change is in effect only in the shell from where it is being called To set the PATH for a specific user, type the below 2 lines in the user's .bash_profile file ($HOME/.bash_profile). PATH=$PATH:/tmp/myshells export PATH To set the PATH for ALL users except the root user, type the following line in /etc/profile export PATH=$PATH:/tmp/myshells Root user is not affected by any setting changes under /etc/profile. To set the path for the root user, we need to modify the root users' .bash_profile (/root/.bash_profile)

For example, if we have shell script named "myshellscript.sh" (with execute permission) we can make it run in the current working directory with the commands $ sh myshellscript.sh (or) $ ./myshellscript.sh If the shell scripts are stored in an executable path, it will save us from typing extra keystrokes. To find the paths that are setup, type $ echo $PATH /usr/bin: /usr/local/bin (more…)

Shell scripts are written to execute a set of commands and to group them. The scripts will have the following special line #!/bin/bash This is an indication that the shell script is used in bash shell and that it should be called for command execution. To know the path of the bash shell, type $ cat /etc/shells (more…)

Shell is an environment around the Kernel providing user interaction. It accepts user commands and convert them to binary code. It is not part of the kernel but uses the kernel to execute the commands. Commonly available shells - BASH (Bourne Again Shell) - CSH (C Shell) - KSH (Korn Shell) All these shells do the same job and the differences come in the form of syntax that these shells use to execute commands and the built-in functions that comes along with it. You can find the shell that is in execution by typing $ echo $SHELL To find all the available shells in the system, type $ cat /etc/shells