User Environments

The Saigon CTT User Environments The Saigon CTT  Objectives Objectives  Construct different login profiles and user accounts  Define, and modify user environments  Security issues The Saigon CTT  Login Shells Login Shells  Shell  an interface between the user and system (kernel).  reads commands from the user and executes appropriate programs  Shell is not implemented as part of OS kernel. The shells is a user-level program. Administrator can replace the standard shell by another shell.  There are many shells on Linux: • Bourne Again Shell (bash) : A superset of the commands of the origin Bourne shell, also implements features of csh and ksh • tcsh : A superset of the commands of the origin C shell • Public-domain Korn shell (pdksh): • zsh : similar to the ksh with many enhencements The Saigon CTT  Environment Files Environment Files  When bash is executed at login time, two initialization files are executed :  /etc/profile : system-wide initialization file  ~/.bash_profile or ~/.bash_login or ~/.profile : personal initialization file  These files :  Contains system commands  Provide a common environment for all users  Set a user-customized environment  Contain user commands and definitions The Saigon CTT  Environment Files Environment Files SYSTEMWIDE: /etc/profile /etc/bashrc USER 1 ~/.bash_profile ~/.bash_login ~/.profile ~/.bashrc ~/.bash_logout ~/.inputrc USER 2 ~/.bash_profile ~/.bash_login ~/.profile ~/.bashrc ~/.bash_logout ~/.inputrc USER 3 ~/.bash_profile ~/.bash_login ~/.profile ~/.bashrc ~/.bash_logout ~/.inputrc The Saigon CTT  Environment Files Environment Files login /etc/profile ~/.bash_profile ~/.bash_profile ~/.bash_login ~/.bash_login ~/.profile ~/.bashrc ~/.bash_logout /etc/bashrc yes yes no no bash start logout The Saigon CTT  /etc/profile Script  The /etc/profile do : o Exports environment variables such as LOGNAME for login name o Exports PATH for the default command path o Set some useful aliases o … The Saigon CTT  User-Specific Initialization Files  The user-specific initialization file(s) are stored in the home directory of the user. These initialization files can perform all or part of the following: o Set the default prompt o Define the default printer o Set default permissions o Tell the shell where to look for new mail (in MAIL=…) o Set noclobber to prevent overwriting of files during redirection o Set the command path to the user’s specification o Set up custom commands The Saigon CTT  Environment Files Environment Files  bash will follow a particular sequence to initiate non-login shells ( e.g open a terminal session or sub-shell bash )  bash will look for the environment file ~/. bashrc and execute it  If BASH _ENV has been assigned with an alternative file, that file is executed The Saigon CTT  Login sequence [...]... the Day (motd)  /etc/motd: print to a user' s terminal after a successful login and before executing the user' s login shell  Keep message short and up to date, otherwise users will stop reading it # more /etc/motd Welcome to Acme's Development System Access to this system is restricted to authorized users only Unauthorized access is prohibited and offenders are liable to prosecution The Saigon CTT ... for security holes  Find out about networked machines (/etc/hosts)  Access the network via telnet or rlogin The Saigon CTT  Summary  Construct different login profiles and user accounts  Define, explain, and modify user environments  Explain security issues ... Each user s environment will be established and customized to reflect their requirements  To see all of your current variable settings (local), execute command set without any options  to see the settings of all of those definitions in your current environment that have been exported (global), use the commands printenv or env The Saigon CTT Message of the Day (motd)  /etc/motd: print to a user' s...The Saigon CTT  Initialization Files Read Process The Saigon CTT  Environment Definitions  Most users will need to modify some of environmental definitions to suit their requirements: PATH=$PATH: Include required search directories PS1=“[\u@\h \W] \$” The interactive shell prompt . Saigon CTT User Environments The Saigon CTT  Objectives Objectives  Construct different login profiles and user accounts  Define, and modify user environments. system commands  Provide a common environment for all users  Set a user- customized environment  Contain user commands and definitions The Saigon CTT  Environment