[newbie] UNIX INTRO: lessons declared open source
Because: o Open source works better than closed source; and o The lessons were developed partly using ksh rather than BASH; and o It is entirely possible that there could be undetected errors; and o Additional contributors will make the lessons better, I hereby declare: ...that everyone is invited and welcome to test the lessons on their Linux installations, particularly using the BASH shell, and to send me any corrections, suggestions for improvements, suggestions for new lessons, or even developed lessons in similar format. Maybe we can make something worthwhile out of these sessions for all new Linux users. (No, I'm not going to go to all the trouble of issuing a GPL at this time... grin...) Note: I'm not experienced enough (by a few lightyears!) to offer similar material on system admin issues. Well, there is the Linux Documentation Project. But that is more task-oriented than training-oriented. There may already be worthwhile efforts of this sort somewhere in cyberspace, which could provide cross-fertilization. Anyone know of any? best wishes, richard myers
RE: [newbie]Change the command line prompt
f bash \w current working directory \W abbreviated current working directory \# command number of the current prompt \! command history number of the current prompt \$ # for root, $ for everyone else By the way, I had a chance to quickly explore the PS1 variable and the startup files in Linux. I found a very curious entry in /etc/bashrc. This is the entire file: -- # /etc/bashrc # System wide functions and aliases # Environment stuff goes in /etc/profile # For some unknown reason bash refuses to inherit # PS1 in some circumstances that I can't figure out. # Putting PS1 here ensures that it gets loaded every time. PS1="[\u@\h \W]\\$ " alias which="type -path" -- Sooo, this is apparently where the prompt is defined on some Linux systems. I also found this entry in the Config HOWTO at http://www.metalab.unc.edu/linux/ so it may actually have come from there (not sure). Note that the same PS1 line appears in /etc/profile so this variable is defined twice. No harm in that, the last definition is used by the system. I don't really like the results of the line PS1="[\u@\h \W]\\$ " ...because I (so far) haven't needed the hostname in my prompt. Therefore I changed my prompt to: PS1="[ \W ] \u \\$ " I think it is a bit less busy. QUESTION: What is the significance of the leading . in .bash_profile and .bashrc ??? ANSWER: It prevents the file from being displayed by the ls statement. To see these files (if they exist), you have to use ls -a This is to reduce clutter, and to protect these important system files from careless tampering. best wishes, richard myers
Re: [newbie] low port privs
On Fri, 30 Jul 1999, David Kammer wrote: Hi All, Odd question. It seems as if only root is allowed to start proccesses with low port numbers like 80 (httpd is not running on my machine). when non-su's try to do this, the port allocation simply fails. My question is is there a way to allow a user to start low port proccesses without giving them full su status? thanks, -dave There are various solutions, but this is one I have been given privileges with. Others can provide more complete info... Sudo - a utility to allow restricted root access Sudo (superuser do) allows a system administrator to give certain users (or groups of users) the ability to run some (or all) commands as root while logging all commands and arguments. Sudo operates on a per-command basis, it is not a replacement for the shell. http://www.courtesan.com/sudo/ best wishes, richard myers
[newbie] UNIX INTRO: Shells, redirection
d command. But now we are faced with a disturbing recognition: ...we COULD have executed pwd just by calling the pwd command directly! $ pwd /u02/home5/rtmyers/testdir $ Why on earth did we go to all of the trouble to call it indirectly by putting the pwd command in another file and then calling that file? And the answer is profound: with this simple procedure, we have created our first simple executable script! We don't have to content ourself with one command, we can put in multiple commands. Also, data structures, and program logic, and other nifty stuff. With these simple techniques, we can build scripts that can do amazing things! Even UNIX! ___________ end ___ best wishes, richard myers
[newbie] UNIX INTRO: Pipes and Redirection
-- Pipes and Redirection -- Someone wrote: : OK...I thought I had it all straight in my mind but : I now find the difference between redirection and : pipes really foggy. Is there something absolute I : can put in my mind to clarify the two? EXCELLENT question!!! -- Digest -- Redirection is a mechanism in the shell that causes the standard input for a program to come from a file rather than from the terminal. It also causes the standard output and standard error to go to a file rather than to the terminal. (Standard output, standard error? Later lesson!) Input redirection is symbolized by the character. Output is the character, and output with append uses the characters. A pipe is a mechanism used by one command to pass information to a second command for processing; a pipe connects the standard output of one command to the standard input of the next, without creating an intermediate file. A pipe is symbolized by the vertical bar | character. -- In-depth -- I don't know of any easy way to learn the difference, other than to practice and see what works: $ echo this thisfile $ cat thisfile this $ We have redirected the output of echo to a file. We can then cat the file and display what is in it. Now try piping from echo to a file: $ echo this | thisfile -ksh: thisfile: cannot execute [Permission denied] $ As you can see, this does not work. However, we can pipe from one command to another: $ echo this | cat this $ This is a redundant operation. It would win the "useless use of cat" award (more about that later). However, it works without generating an error (important for our purposes), and this next step proves that *echo* isn't displaying "this" to the screen, *cat* is. Now lets try to redirect to cat and see what happens: $ echo this cat $ Well, what happened to our output? It didn't appear on the screen! We can find it if we look for redirection to a file using cat: $ cat cat this $ Aha! In the previous command we redirected the string "this" to a newly-created file called cat, and we can display that file with cat. As a general guideline, then, redirection seems to work with files, and piping works with commands. It does get a bit more complicated later on, but for now that is a good way to tell the difference. Lets try one more example. The wc command does word counting, and this particular behavior is turned on with the -w switch. Thus: $ echo this | wc -w 1 $ We have echoed one word to wc -w. $ echo this that | wc -w 2 $ $ echo this that other | wc -w 3 $ ...and a two, and a three... Now lets try redirecting three words to wc -w (instead of piping). $ echo this that other wc -w $ No output. No error. That means our command was successful, but maybe didn't do what we wanted (since we were expecting output to the screen). We can find the file created with redirection by using ls: $ ls wc $ And now for the mysterious part: $ cat wc this that other -w $ Our words were not counted, they were redirected into a file which has the filename wc. But how did that -w get in there? Ahhh, but that is the subject of a later lesson! ___ end ___ Errata: it IS possible to pipe to a file. How? Because (as we saw in the last lesson) a file can become a command. But piping to a user-created command is an advanced technique, and we aren't going to explore that right away. best wishes, richard myers
Re: [newbie] UNIX INTRO: Shells, redirection
$ thisfile -ksh: thisfile: cannot execute [Permission denied] On Thu, 29 Jul 1999, Andy Goth wrote: So I was right. I was expecting pdksh, though (the Public Domain Korn SHell). It appears that the maillist switched the order of my two posts. Yes, Korn Shell. In my experience pdksh is not a good substitute for ksh (although my experience was years ago; not sure of the current status). And what of the C Shell? I have used the C Shell, and it provides a nice interface. However, csh is worse than worthless for creating scripts: quote Unix Support frequently advises people not to use /bin/csh. Here is the classic document by Tom Christiansen on why you shouldn't use it for scripts. Csh Programming Considered Harmful Resolved: The csh is a tool utterly inadequate for programming, and its use for such purposes should be strictly banned. I am continually shocked and dismayed to see people write test cases, install scripts, and other random hackery using the csh. /quote See the complete article at: http://vega.ing.iac.es/~cfg/notes/pub_notes/csh.html ...I read about one version called "tcsh" in a Linux book. I've heard it is improved. I'd do some research before I started using it, however. The above URL is a good place to start, it mentions tcsh. Isn't there a convention that the first line of all shell scripts should be a comment identifying which shell it is to be run with? I believe I have seen things like: #!/bin/sh In the UNIX world, there are basically two types of shell scripts-- those based upon the Bourne Shell (including Korn Shell and BASH), and those based upon the C Shell. The common shell language for writing portable scripts is the Bourne Shell. Advanced features of other shells are to be avoided unless the script is never expected to leave the target system. There may be other considerations for Linux. It seems that BASH has become pretty much a standard. The #! convention is an interesting story. Too long for posting here; I refer you to: unix/faq Digest part 3 of 7 by Ted Timar - [EMAIL PROTECTED] It is a regular posting in comp.unix.shell, or check out: http://www.faqs.org/faqs/by-newsgroup/comp/comp.unix.shell.html Here is just an excerpt: quote 3.16) Why do some scripts start with #! ... ? [...] The Berkeley folks had a neat idea to extend how the kernel starts up programs. They hacked the kernel to recognize the magic number `#!'. (Magic numbers are 16-bits and two 8-bit characters makes 16 bits, right?) When the `#!' magic number was recognized, the kernel would read in the rest of the line and treat it as a command to run upon the contents of the file. With this hack you could now do things like: #! /bin/sh #! /bin/csh #! /bin/awk -F: This hack has existed solely in the Berkeley world, and has migrated to USG kernels as part of System V Release 4. [...] /quote best wishes, richard myers
[newbie] General configuration, tool comparison questions
What is the best way to learn system configuration and administration skills for a home-based Linux system, without feeling like I am on a treasure hunt through the Linux Documentation Project files? I'm somewhat experienced with Unix, but not experienced with system administration and not experienced with Linux. I'm in the process of configuring Mandrake 6.0. I have used the Configuration HOWTO, and found that it had a lot of excellent information. However, I am impatient with brief, introductory information. I want more technical material. Why do I configure it this way? What other options are available? Does anyone have recommendations (books, online documents, URL's, other maillists, etc.)??? ALSO-- we have a number of choices available when selecting basic tools in Linux. Is there a good source for comparing such tools for feature-set, ease of configuration and use, etc. ??? I'd be happy to spend some money for the right books-- I already have Linux for Dummies, and Linux in a Nutshell. Unfortunately they are more introductory than in-depth. Other recommendations welcome. I've checked out book reviews at fatbrain.com, but most of the titles that are recent publication-date and sound good aren't available yet. best wishes, richard myers
Re: [newbie] Oh, yeah
-rw-rw-r-- 2 rtm465 0 Jul 27 02:22 hardlink_1 -rw-rw-r-- 2 rtm465 0 Jul 27 02:22 hardlink_2 lrwxrwxrwx 1 rtm465 10 Jul 27 02:35 softlink_1 - hardlink_1 Whoa! Notice that our soft link is created with WORLD WRITE permissions (the 3rd "w" in the group of "rwx's" in the line above). Doesn't matter, the symlink REALLY inherits the permissions of whatever it points to. Also notice that the symlink has 10 bytes. Why is that? Now we will put something into the file that the symlink points to: $ echo another string softlink_1 $ So, what happens if we cat the contents of all the files in the directory? $ cat * another string another string another string $ $ ls -l total 6 -rw-rw-r-- 2 rtm 465 15 Jul 27 02:35 hardlink_1 -rw-rw-r-- 2 rtm 465 15 Jul 27 02:35 hardlink_2 lrwxrwxrwx 1 rtm 465 10 Jul 27 02:35 softlink_1 - hardlink_1 $ All of our files now contain 15 bytes-- 14 for the string, plus one. Well, EXCEPT for the symlink. It still contains 10 bytes. That is because it is just a pointer to another filename (whether that filename exists or not). If we remove the first hard link, see what happens: $ $ rm hardlink_1 $ $ ls -l total 4 -rw-rw-r-- 1 rtm 465 15 Jul 27 02:35 hardlink_2 lrwxrwxrwx 1 rtm 465 10 Jul 27 02:35 softlink_1 - hardlink_1 $ $ cat * another string cat: cannot open softlink_1: No such file or directory $ Since our symlink points to a non-existant filename, we cannot display contents. BUT, the contents still exist under a different filename. BUT-- the symlink still points to that filename. If we create that file anew: $ echo some other NEW stuff in our file hardlink_1 $ $ cat * some other NEW stuff in our file another string some other NEW stuff in our file $ Neat stuff, huh? This is Unix. best wishes, richard myers
Re: [newbie] Oh, yeah
On Tue, 27 Jul 1999, Richard Myers wrote: Neat stuff, huh? This is Unix. best wishes, richard myers On Tue, 27 Jul 1999, darkknight wrote: : ) Ever thought about teaching? We, I taught an online college-level Intro to Unix course for several years. Gave it up because (1) the college didn't support it well enough, and (2) I make ten times as much money working for Lucent Technologies. I always had trouble grasping the diferrence between hard links and soft (symbolic) links, untill now. And I was'nt even the poster of the message. cool , thanks alot, you really have patients and should consider teaching as a career. Great stuff indeed, Unix has always facinated me but I thought it too hard for me to grasp. More lessons like that and there might be hope for me yet. I shure am glad I make it a habbit to at least skim through each and every post. Thanks alot, John Love [EMAIL PROTECTED] Hmmm. Glad it helped. Maybe we should do some quickie Unix-command-line intro lessons online. QUESTION: should it be on this list, or would it be better to start a new, separate maillist? Or should we just try a few easy lessons, and see how it goes, with the option to move elsewhere later? What say, everyone? best wishes, richard myers
Re: [newbie] Oh, yeah
On Sun, 25 Jul 1999, Andy Goth wrote: Then what are hard links good for? There are two applications which do something similar. Call them xyzzy and plugh. xyzzy gives you a help menu, but plugh is for expert users who don't need (and don't want) a menu. I write a better application-- better than both of them, but it incorporates the features of both. Everyone starts using my application instead of the two old ones. And I include a flag that you can set-- either menu, or no menu. But my users get tired of always having to turn that darn menu on or off. Soo, I come up with this great idea. I create two names (make that two *file* names) for the new application, xyzzy, and plugh. These are hard links to the same file. They both do the same thing-- launch my program. Well, they do one thing different. They place different values into one special variable made available to my program, which keeps track of what filename was used to launch my program. And those two different values are: xyzzy, and plugh. In my application I test whether it was called with the command xyzzy. If so, I make it act like xyzzy, menu and all. If my application was called by the name plugh, I know this must be an expert user-- she's calling it by the name of the old program she used to use-- and so for her my application automatically provides no menu to take up screen space and get in the way. Hard links make both my user groups happy. (Honesty in posting-- I didn't come up with any of these ideas, but I think they are nifty. ;-) Trivia-- xyzzy and plugh are actually magic words from the 70's computer game "advent". best wishes, richard myers
[newbie] mount partition problem solved!
I posted this in a newsgroup, but since it solved a problem I had earlier asked about here, I thought the solution might be of interest to someone on the list: - From [EMAIL PROTECTED] Sat Jul 24 21:44:48 1999 - Date: Sat, 24 Jul 1999 21:25:05 -0600 - From: Richard Myers [EMAIL PROTECTED] - Newsgroups: comp.os.linux.setup - Subject: Re: mount problem-- still not working On 22 Jul 1999, Colin Watson wrote: In article 7n6qum$[EMAIL PROTECTED], [EMAIL PROTECTED] wrote: Colin Watson ([EMAIL PROTECTED]) wrote: : Have you tried using the full syntax for mount, that is: : mount -t ext2 /dev/hda9 /mnt/win2 [...] Does creating a completely new partition and mounting it work? No. But I solved the problem-- it was a lot more stubborn than I had expected. I went looking for a partition table problem when I saw in a help file or man page that logical partitions should start numbering at 5-- mine started at 6. (I had wondered about this, but decided earlier that I didn't know enough to consider it a problem.) Somehow I had a "hidden" partition, /dev/hda5, which was only a fraction of a megabyte. It was so tiny that fdisk, partition magic, and even Linux itself did not see it. I didn't discover it until I ran cfdisk, which showed it plain as day. Such a small sliver of free space, guess I might have noticed if I had really studied those numbers carefully. But it was enough to mess up the swap file, and some other stuff, because Linux couldn't tell if it should be assigned as /dev/hda9 or /dev/hda8. I removed the tiny partition and re-installed Linux, and things are working much better now. Thanks for the help! Lesson: look at a stubborn problem in a number of different ways, using a number of different tools. The solution may jump out at you just when you're about to pull your hair out!! ;-) And with experience, I will know that my vague unease about the numbering starting at /dev/hda6 instead of /dev/hda5 is something to prompt quick investigation next time. best wishes, richard myers
Re: [newbie] hardware
On Thu, 22 Jul 1999, [EMAIL PROTECTED] wrote: Ok, I'm gonna be upgrading a large amount of my hardware and need to make sure I buy linux compatible hardware. Most notable I'm gonna be getting a new modem, vid card, NIC, and something else I seem to be missing. Is there a website I can go to and check if all the hardware I'm looking into getting is supported? Wise move. You'll want to memorize this URL, or build a link to it on your web page: http://www.metalab.unc.edu/linux/ The specific document you want is, Plain text: http://metalab.unc.edu/pub/Linux/docs/HOWTO/Hardware-HOWTO ...or, HTML: http://www.metalab.unc.edu/linux/HOWTO/Hardware-HOWTO.html There are also a few special-purpose hardware compat web sites, I'm away from my list right now but maybe someone else can help out here. best wishes, richard myers
Re: [newbie] Oh, yeah
On Fri, 23 Jul 1999, Andy Goth wrote: I've spent long sleepless nights before fixing the system.ini file after moving programs from C:\Program Files to D:\Prog. Luckily, I had a utility to rename most references that went to my CD-ROM drive after it changed letters. In Linux, such a thing isn't necessary since drives are referred to by their real names, not by arbitrary letters. I think that the problem is not the "arbitrary letters", but the fact that these letter designations get "bumped" when new hardware is added. rant There is a user interface analysis website (ask me for the link, if interested) that strongly suggests Microsoft has used graphic designers to create their interfaces so that they look pretty, even when this renders them semi- or non-functional. Shouldn't be any surprise. If your CDROM could just stay as your D: drive, and your next hard drive could become E:, the upgrade problems would be fewer. Of course then installation software would have to query each storage device, "are you a hard drive or CDROM?" I think this identification process is common sense now, but when the drive scheme was set up, Microsoft's simplification of the Windows installation procedure was probably more important to them than any provision for upgrading. "What, have a CDROM in between non-consecutive hard drive letters? That's not pretty enough for our customers!" /rant best wishes, richard myers
Re: [newbie] CRASH!
On Mon, 19 Jul 1999, Ramon Gandia wrote: [...nfs discussion deleted...] All of this is best done in console and not in X or you may incur the wrath of Athena, the goddesd of hard rocks. ^^^ I know, this is the *daemon* of goddesses, right? grin best wishes, richard myers
Re: [newbie] OSS
On Tue, 20 Jul 1999, Bert Bullough wrote: Greetings all. I have just successfully installed the OSS Drivers for the Turtle Beach Montego cheers I tried it out with an AVI movie and some Mp3z. These both work great but when I play a wave file the audio is choppy, high-pitched, and distorted. Ideas? Isn't it still beta software? Last time I checked it out (few weeks ago), it was beta and they charged a small fee for it to keep it working past the (20 minute?) cutoff code. I'll be trying it in a few more weeks, hope it is finalized by then. best wishes, richard myers
Re: [newbie] Filesystem gets badly corrupted !
On Sun, 18 Jul 1999, Khalid wrote: Hi To all I have just installed Mandrake 6.0 on an IBM Thinkpad 1400. KDE freeze too often, I always need to reboot, but at boot time Linux tells me that the file system is corrupted and that I need to run a fsck. 2.2.9? Not sure if this is related, but check out: http://lwn.net/1999/0624/a/ac-corruption1.html (excerpt) --- From: Alan Cox [EMAIL PROTECTED] Ok this is the distilled info so far 2.2.7 - 2.2.9 broke a small number of systems. --- I didn't follow this, you may find more info on Alan Cox's site. Good luck, richard myers
Re: [newbie] lost info in bash prompt
On Sat, 17 Jul 1999, pauljw wrote: I did some fiddling and had to put my home (user, not root) directory back in place from a backup. Happily, everything worked save for the bash prompt. It looks like: bash-2.03$. It used to show the user name and the current directory. How can I get that back? TIA, -Paul- On Sun, 18 Jul 1999, Richard Myers wrote: I had a chance to explore the PS1 variable and the startup files in Linux. I found a very curious entry in a file called bashrc in the /etc directory. This is the entire file: -- # /etc/bashrc # System wide functions and aliases # Environment stuff goes in /etc/profile # For some unknown reason bash refuses to inherit # PS1 in some circumstances that I can't figure out. # Putting PS1 here ensures that it gets loaded every time. PS1="[\u@\h \W]\\$ " alias which="type -path" -- Sooo, this is apparently where the prompt is defined. It sure would be interesting to know who wrote the notation there-- anyone know if this is in a /etc/bashrc file in RedHat Linux? Note that the same PS1 line appears in /etc/profile so this variable is defined twice. No harm in that, the last definition is used by the system. Note that \$ gives a # if you are root, otherwise it will print a $ I don't really like the results of the line PS1="[\u@\h \W]\\$ " ...because I (so far) haven't needed the hostname in my prompt. Therefore I changed my prompt to: PS1="[ \W ] \u \\$ " I think it is a bit less busy. The normal order of startup that I am familiar with (that is, the order in which the files are read and executed) would be: /etc/profile ~/.bash_profile (where ~/ represents your home directory). ~/.bashrc But with a /etc/bashrc file, the order is going to be: /etc/profile /etc/bashrc ~/.bash_profile ~/.bashrc (again, where ~/ represents your home directory). Therefore, you can set global system variables (that is, variables that are defined for all users) in the two files in /etc, and these variables can (normally) be redefined in the users' files. QUESTION: What is the significance of the leading . in .bash_profile and .bashrc ??? ANSWER: It prevents the file from being displayed by the ls statement. To see these files (if they exist), you have to use ls -a This is to reduce clutter, and to protect these important system files from careless tampering. best wishes, richard myers
Re: [newbie] Problem...FreeBSD?
On Sun, 18 Jul 1999, Mark E Hood wrote: I've kinda been fooling with FreeBSD, too. In what ways is it different than linux? Is it better? worse? Check out: http://slashdot.org/article.pl?sid=99/07/02/0537230mode=thread (Slashdot synopsis) "In what has got to be one of the better pieces on the Linux vs. BSD debate Wes Peters talks about both OS's, the strengths and weakness of each, and how they live together to form a symbiotic circle. " best wishes, richard myers
