For 2023 - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.
Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!
I am also active in many other area and still look after a lot of web sites - you can find an index ((here))
Supporting users on Linux and Unix
Q: If you're the administrator on a Linux or Unix system and you want to help a user look after some of the files and directories, or run applications, under their own account, what's the best login to use?
A: You should be logged in as if you were the user him/herself
A: Because you want the ownerships of any file system objects you create, and processes, and any logs to be assigned back to that user, and you want the environment (PATH etc) to be the one that the user would be using as well.
Q: Does this mean I have to ask the user to give me his / her password then?
A: No. certainly not. Here's what you should do:
a) Log in as normal through YOUR OWN user account
b) Use the command su -
to become the administrator ... and, yes, you need the root password to do this
c) Then use the command su - george
to become the user george. You will NOT be asked for George's password, since the administrator can "su" to any other account without giving one - he/she has already logged in and gained sufficient authority via the root account.
Q: Is that real a minus sign after the su command? Is it needed?
A: Yes, it is, yes it is. It tells the su command to set up a new environment for you using the settings for the user that you're about to become. Without it, you'll be running with your original users environment, but with the new user's authorities. Occasionally that's convenient if you have a lot of aliases but it can leave some huge security loopholes and it means that you won't be seeing the system in the same way the user will, meaning that you won't (for example) be able to exactly reproduce any problems that he's calling for support on. (written 2006-04-13, updated 2006-06-05)
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articlesA161 - Web Application Deployment - Users and Groups 
Functions and commands with dangerous names - (2005-08-11) 
File permissions of Linux and Unix systems - (2005-08-31) 
Setting up a new user - Linux or Unix - (2008-03-26) 
User and Group settings for Apache httpd web server - (2008-04-22) 
Looking for files with certain characteristics (Linux / Unix) - (2008-05-22) 
The Longest Possible Day - (2008-08-26) 
sstrwxrwxrwx - Unix and Linux file permissions - (2008-11-23) 
Ruby, Perl, Linux, MySQL - some training notes - (2008-11-23) 
Ask the Tutor - Open Source forum - (2009-03-25) 
Choosing a railway station fairly in PHP - (2009-04-04) 
Always use su with minus. And where do programs come from? - (2009-05-27) 
Mistaken identity? - (2009-07-22) 
Root is root for a reason! - (2009-11-03) 
su or su - ... what is the difference? - (2010-02-17) 
Linux Web Server - User Roles, User Accounts, and shared administration - (2013-03-16)
Some other Articles
Presentation, Business and Persistence layers in Perl and PHPName Services - telling your LDAP from your DNSA couple of days awayStaying in the countrySupporting users on Linux and UnixIran has enriched uranium ...Mirroring a dynamic siteLetter BoxesMore or less on the edge of the pageWhy are maps rarely to scale?
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This is a page archived from The Horse's Mouth at
the diary and writings of Graham Ellis.
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