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Training, Open Source Programming Languages |
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| For 2023 (and 2024 ...) - 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 Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own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)) |
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Mistaken identity?
I asked who I was logged in as yesterday ... and I got two different answers: [melksham ~]# who am iWhen you log in to a Unix or a Linux box, you give an account name (and password, I hope!) and you're given a user account name / identity. Or so you think - but really you have two identities, your real and your effective id. If you use a command such as su to get a new identity, your effective id changes, but not your real id ... and that's what had happened with the report above. There is a good reason for this ... the difference between real and effective ids is used within programs too - operating system programs such as the passwd program. On one hand, users cannot possibly be allowed to write from their normal accounts to the file that contains encoded passwords - think of the security risk, yet on the other hand they must write to that file if they're going to be changing their password. The conundrum is neatly overcome by having the passwd program set up with a setuid bit, which means that while you're running it, you have an effective root id while your real id remains as the user you logged in as. We tell you more about su and why you should always run su - on our Linux Admin Introduction. (written 2009-07-22, updated 2009-07-23) Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles A161 - Web Application Deployment - Users and Groups[409] Functions and commands with dangerous names - (2005-08-11) [431] File permissions of Linux and Unix systems - (2005-08-31) [683] Supporting users on Linux and Unix - (2006-04-13) [1592] Setting up a new user - Linux or Unix - (2008-03-26) [1619] User and Group settings for Apache httpd web server - (2008-04-22) [1650] Looking for files with certain characteristics (Linux / Unix) - (2008-05-22) [1773] The Longest Possible Day - (2008-08-26) [1902] sstrwxrwxrwx - Unix and Linux file permissions - (2008-11-23) [1904] Ruby, Perl, Linux, MySQL - some training notes - (2008-11-23) [2103] Ask the Tutor - Open Source forum - (2009-03-25) [2117] Choosing a railway station fairly in PHP - (2009-04-04) [2203] Always use su with minus. And where do programs come from? - (2009-05-27) [2491] Root is root for a reason! - (2009-11-03) [2639] su or su - ... what is the difference? - (2010-02-17) [4045] Linux Web Server - User Roles, User Accounts, and shared administration - (2013-03-16)
Some other Articles
Hot Tap at West Wilts ShowExtracting real data from an exported file in PHP or Perl Turning potential customers away See us at the West Wilts Show Mistaken identity? What does x on a linux directory mean? How much space does my directory take - Linux Melksham Carnival Parade - the people Standing on the corner, Melksham Carnival Variable scope - what is it, and how does it Ruby? |
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Link to page ... 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96 at 50 posts per pageThis is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.
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