SOCS Inside-Out

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LAST UPDATE: Friday, 19-Mar-1999 19:59:21 EST

general - X - SOCS - defaults and misc

	General Computing Tips:: Oddities and Troubleshooting
	- Vincent Stephen-Ong

It is important to note that the entirety of this section really expects that you have some Unix and/or X literacy, especially for the why it works explanations.

General Oddities

There are a couple of things that are generally odd about the way things work on the systems available at SOCS, particularly on the Unix machines if you are not used to their idiosyncrasies

gcc Optimization Problems
"I'm compiling perfectly good C code and I'm not getting the expected results!"
- symptoms:
  - You write a C program, compile it unoptimized (i.e.: with no special command-line arguments), and it works fine. You then recompile the program with optimizations (e.g.: gcc -O2) and it stops working, core dumps, or otherwise screws up.
- examples:
  - ```
  #include <stdio.h>
  
  main() {
      int i;
      for (i=1;i<32;i++)
          ;
      printf("%d\n", i);
  
  }
```
- ```
#include <stdio.h>
#include <stdlib.h>
#define N 8
struct node {
    struct node*next;
};
static struct node *first;
static struct node nodes[N];
int main (void)
{
    struct node **p;
    int i;
    p = &first;
    for (i=0; i<N; i++) {
	*p = nodes + i;
	p = &nodes[i].next;
	/* rand (); */  /* uncomment this line and it works */
    }*p = NULL;

    puts (first==nodes
	  ? "this is what I expected"
	  : "what is going on here?");
    return 0;
}
```
- solutions:
  - Obviously, if you compile with no optimizations, you won't have this problem, but this isn't really a viable alternative.
  - The gcc 2.8.x line is known to have many, many bugs, especially in its optimizer. If you really need a C++ compiler, try egcs.
  - Try compiling with "-O" only or add the "-fno-strength-reduce" flag; it might solve the problem.
  - Switch or downgrade to a compiler in the gcc 2.7.x line, it has much fewer bugs, although the -O2 bug does seem to affect it in case #2. It seems that using -fno-strength-reduce is a good idea, in general.
- additional notes:
  - Obviously this is a bit of a more technical issue... Some things you might want to know are:
    - How to check which version of gcc I'm using:
```
% gcc --version 
```
    - How exactly should I be compiling stuff?
      Well, if you're compiling unoptimized code, then you won't have any problems. The correct syntax is:
```
% gcc filename.c
```
      If you're compiling optimized code, the best way to avoid these problems (if you can't switch compilers) is:
```
% gcc -O -fno-strength-reduce filename.c
```
Backspace vs Delete
"My Backspace key doesn't work!"
or "My Delete key doesn't work!"
or "Why the hell do Backspace and Delete act so damn weird?"
- symptoms:
  - You hit backspace, and it doesn't give you what you expected. Or, you hit delete, and it doesn't give you what you expected. By "not what you expected" I mean that it either deleted the wrong character, didn't do anything, or produced a weird garbage character (like "^H") on the screen.
- examples:
  - At the prompt, type a bunch of stuff, and move the cursor to somewhere in the middle of the text. Next, hit the Backspace key a few times, watch what happens, then hit the Delete key a few times (and watch what happens).
  - ytalk someone and try hitting Backspace and Delete and see what happens.
  - Frustrating, isn't it?
- solutions:
  - Try adding
```
stty erase ^h
```
    to your login script.
  - Try adding
```
keycode 14 = BackSpace
keycode 111 = Delete
```
    to your .loadkeys and make sure
```
loadkeys ~/.loadkeys
```
    is in your login script.
  - Try adding
```
keycode 22 = Delete
keycode 107 = BackSpace
```
    to your .xmodmap and make sure
```
xmodmap ~/.xmodmap
```
    is in your .xinitrc and/or .xsession
  - If you use emacs, add these lines to your .emacs:
```
;; for X
(cond (window-system
       (global-set-key [delete] 'delete-char)
       (global-set-key [backspace] 'backward-delete-char)
       ))
;; for non-X
(cond ((equal window-system nil)
       (global-set-key [(control h)] 'backward-delete-char)
       ))
```
- why it works:
  - The deal is (basically) that way back when, DEL (delete) was used to mean ignore-this-character. DEC took it to mean erase-the-previous-character, and put the DEL key on top of the <entergt; key on VTx00 terminals. IBM on the PC but backspace (C-H). It's a godawful mess, and one of the worst things about UNIX, IMHO.
    Thanks to Louis Raphael for this explanation.
    In other words, there were two different standards established at to what "the key above <enter>" should do and this inconsistency is still present in Unix.
  - The stty line says to treat the Ctrl-H keysequence as meaning "erase".
  - The loadkeys solution only works at the console and it physically assigns the keys "14" and "111" to delete and backspace in the appropriate way.
    This is the console equivalent of xmodmap.
  - The xmodmap solution only works under X and it physically assigns the keys "22" and "107" to delete and backspace so that "the key above <enter>" deletes the character before the cursor, and <delete> deletes the current character.
    This is the X equivalent of loadkeys.
  - The emacs solution applies only for emacs, naturally. It sets the <delete> and <backspace> keys appropriately under X. Unfortunately, it is impossible, at the console, to tell the difference between a C-h and "the key above <enter>" since "the key above <enter>" sends C-h. As a result, we rebind C-h to backward-delete-char. This means that if you want the "usual" C-h functionality (help), you'll have to either rebind it to something else or invoke it via M-x help.
XON/XOFF (Flow Control)
"In one of my xterms (or the console), the keyboard won't respond!"
- symptoms:
  - Your keyboard stopped responding to keypresses in one of your xterms. You may have previously hit a bunch of (random) keys.
- examples:
  - Hit <Ctrl>-S. Now, try and type stuff. You'll find that nothing appears on your screen.
- solutions:
  - Hit <Ctrl>-Q.
- why it works:
  - In software handshaking protocols, it is necessary to transmit extra data in order to control the sending and receiving of data along a channel.
    In an xterm and at the console, <Ctrl>-S sends the "XOFF" signal which, appropriately, signals a stop of character/data transmission ("XOFF"="xfer off"="transfer off"). Symmetrically, <Ctrl>-Q sends the "XON" signal which signals resumption of output.
Filenames with special characters
"I can't view/edit/delete/access this weirdly-named file!"
- symptoms:
  - You cannot view, edit, delete, or in anyway access a certain file. Error messages can be quite diverse.
- examples:
  - Type the command
```
% echo "this is a test" > <test>
```
    to create a file called
```
<test>
```
    in your directory.
  - Now, if you try to view the file with less, you'll get an error message:
```
% less <test>
Missing name for redirect.
```
- solutions:
  - If your shell supports automatic filename completion, try using that. (Type the first few letters of the file name, then hit <Tab> or <Esc>)
  - Try typing the name of the file enclosed in double quotes (").
  - Try placing a forward slash "\" in front of "strange" characters, and enclosing the resulting name in double quotes (").
- why it works:
  - Certain special characters are assigned special meaning in different Unix shells. When these characters appear in a file name, you have to specially indicate that they are to be treated literally (and not given their special meaning).
    In the above example, the < and > signs are usually used for input and output redirection. Since they appear in the filename, you must tell the shell to treat them literally. Different shells have different mechanisms for this, but successfully read the file in the above example with either:
```
% less "<test>"
```
    or
```
% less \<test\>"
```
    under all of tcsh, csh, and bash.

X-Windows Oddities

X can sometimes be a bit of a temperamental beast; here a few taming tips.

Fuzzy screens
"My screen is all fuzzy and out of focus!"
- symptoms:
  - The screen is fuzzy and out of focus.
- solutions:
  - Hit
    - <Ctrl> <Alt> + (that's "control alt plus") or
    - <Ctrl> <Alt> - (that's "control alt minus")
    to change the resolution to a different, stable resolution.
    You can also use these keys to switch between a stable resolution and the fuzzy one until the fuzzy one stabilizes.
  - Hit
    - <Ctrl> <Alt> Fx (where Fx is a function key)
    to switch to another virtual console. Switch back to your X console with (at SOCS) <Ctrl> <Alt> F2.
    Continue this until the fuzzy screen stabilizes.
- why it works:
  - Not sure really. It probably has something to do with an slightly incorrectly-specified monitor refresh rate in the X-Windows configuration, but we're not sure.

SOCS Oddities

There are a few things that you will find, over the course of your time at SOCS, don't quite operate the way you might expect or that operate in a way that is peculiar to SOCS. The purpose of this section is to save you some frustration and point them out for you ahead of time.

Missing C function prototypes on SOCS' SunOS 4 machines
"My C code is perfectly good but the compiler keeps complaining!"
- symptoms:
  - You compile perfectly good C code with the -Wall option and you encounter a number of warning messages regarding implicit declarations. The compile succeeds anyway and the program seems to work.
  - You try compile perfectly good C code you a encounter a number of error messages regarding undeclared identifiers. The compilation fails.
  - Some combination of the above.
- examples:
  - Given this classic C program (line numbers added):
```
1   #include <stdio.h>
2   #include <stdlib.h>
3
4   int
5   main(int argc, const char *argv[])	    
6   {
7       printf("Hello world!\n");
8
9       return EXIT_SUCCESS;
10  }
```
  - Attempts to compile it on a SunOS machine, result in the following response from gcc (on lisa):
```
[lisa] [/u3/ugrad/zibalatz/tmp/test] gcc -Wall helloworld.c
helloworld.c: In function `main':
helloworld.c:7: warning: implicit declaration of function `printf'
helloworld.c:9: `EXIT_SUCCESS' undeclared (first use this function)
helloworld.c:9: (Each undeclared indentifier is reported only once
helloworld.c:9: for each function it appears in.)
helloworld.c:10: warning: control reaches end of non-void function
```
- solutions:
  - 1. Download protos.h.
    2. Rename it (if it isn't already) to protos.h.
    3. Copy or move it to the directory that contains your C program.
    4. In your C program's source file, include a line at the top of your program that reads:
```
#include "protos.h"
```
    5. Add additional function prototypes and/or macro definitions as necessary. You can use the man pages to find out what the correct function prototype should be.
  - Compile under another platform (such as one of the Linux Pentiums). This will only work if your program does not rely on libraries or architectural considerations that would necessitate the use of a SunOS machine.
- why it works:
  - SOCS' SunOS 4 machines are missing several key function prototypes and macro declarations. This is believed to be a bug in SunOS4.
    - implicit declaration means that gcc did not find a function prototype for a function that is being used. In the example, it complains because it could not find a function prototype for printf(). Hence, the function is declared implicitly (as opposed to explicitly in the form of a function prototype).
    - undeclared identifier means that gcc encountered a non-function token which it did not recognize. It assumes that it is an identifier (variable name, label name) of some kind but that you did not declare it. In the example, it complains because it could not find the declaration of EXIT_SUCCESS.
  - protos.h provides some but not all of the missing prototypes. You will still encounter the occasional warning message. Add your own function prototypes (with the extern prefix) to this file as you encounter them. You can check the man pages for the functions which generate warnings in order to figure out what their prototypes should be.
Getting automatically logged out from your machine after a certain amount of idle time
"I logged into a machine, went for lunch, and when I came back, I was logged out!"
- symptoms:
  - After a certain amount of time idle on a machine, all of your applications close and you are returned to the xdm login screen.
- solutions:
  - This is not a bug. Don't stay idle for excessive amounts of time. If you are going to physically occupy a machine, then make use of it.
- why it works:
  - There is a program running on the Linux Pentiums called xautolock.
    - After 10 minutes of inactivity, it automatically starts a screen saver.
    - After 15 minutes of inactivity, an "auto-logout button" appears on the screen. If someone clicks it, the idle user is logged out.
    - After 20 minutes of inactivity, the idle user is automatically logged out.
    The reasoning behind this is that it is not encouraged to login to a machine, password lock it, and then leave for lunch because other people are prevented from using the machine while you do so.
    The script is intelligent enough to detect when there are other machines available in the labs and, in this case, the idle times are somewhat longer.
Getting automatically logged out from your machine suddenly and for no apparent reason
"I was in the middle of typing and suddenly I got logged out!"
- symptoms:
  - You are not idle and may be in the middle of typing or doing other work when suddenly all your applications close and you are returned to the xdm login screen.
- solutions:
  - This is a bug, and we don't know why it happens. If you do, please contact systems staff.
- why it works:
  - Nobody knows- it must be a bug somewhere, someplace, but we don't know what it is. It is not related to the above-mentioned auto-logout feature.
Attempts to login to a Pentium with a full quota
"My quota is full and I can't login to a Pentium!"
- symptoms:
  - Your disk quota is full and you cannot login to a Pentium.
- solutions:
  - Login from a terminal or other remote location and either delete enough files to drop below quota, or move them to secondary storage (i.e.: zip or floppy disk), or compress them using gzip or compress.
  - A good place to look for wasted space is in ~/.netscape/cache This is where your Netscape cache is stored and it can be safely purged.
- why it works:
  - When your quota is full, you will not be allowed to login to a Pentium. This is not a bug; it is an intended feature of the SOCS systems.
The newsreader tin displays user's email address with two @ signs instead of one
"Why is tin garbling my email address?"
- symptoms:
  - All the messages you post with tin contain a mangled version of your email address. Specifically, there are two @ signs instead of one.
- examples:
  - If my user name is ncc, posts made with tin appear to be signed by ncc@@cs.mcgill.ca
- solutions:
  - There are none.
- why it works:
  - This bug seems to occur only for a few users. It happens to Nick Cabatoff, for instance, but it doesn't happen to me (Vincent Stephen-Ong). We don't know why it happens, or how to solve it. Consider it a feature since it means spammers will have a harder time reaching you!

SOCS Defaults and Miscellaneous Issues

It is quite useful to be aware of what the default configuration files are and where they are located on the SOCS systems.

Shell Configuration
"Why does tcsh/bash/csh not operate the way I expect it to?"
or "Where can I find examples of shell configuration/startup files?"
- For tcsh:
```
/usr/socs/Cshrc
```
  is the default .cshrc
```
/usr/socs/Login
```
  is the default .login
- For bash:
```
/usr/socs/Profile
```
  is the default .profile, but it is not available on all machines. You may want to keep a copy in your home directory and source it when you can't find the global one.
Emacs Configuration
"Why do I get this weird behaviour from emacs despite my .emacs settings?"
or "Where can I find examples of emacs configuration?"
- By default, emacs always runs the default.el file before it runs your .emacs if it can find it in its load path.
  On the SOCS systems, this is located at:
```
/usr/local/lib/emacs/site-lisp/default.el
```
  You can easily override this with a few command-line options. I would recommend aliasing emacs to:
```
emacs -q -l ~username/.emacs
```
  if you don't want the SOCS default.el to be loaded.
X-Windows Configuration
"What happens when X starts up?"
- The global X intialization file can be found (on the Pentiums) here:
```
/var/X11R6/lib/xinit/xinitrc
```
- To create your own startup file, copy this file to your home directory and rename it to ".xinitrc" You can then edit this file and thereby set your configuration. Make sure that the file is readable and executable.
FVWM and TWM Configuration
"What happens when FVWM or TWM or TVTWM starts up?"
- The global FVWM resource configuration file can be found (on the Pentiums) here:
```
/var/X11R6/lib/fvwm/system.fvwmrc
```
  The global TWM resource configuration file can be found (on the Pentiums) here:
```
/var/X11R6/lib/fvwm/system.twmrc
```
- To create your own configuration file, copy the appropriate file to your home directory and rename it to ".fvwmrc" or ".twmrc" You can then edit this file and thereby set your FVWM or TWM configuration. Make sure that the file is readable and executable.

Indices
Contents - Verbose - Glossary

feedback
Last modified: Friday, 19-Mar-1999 19:59:21 EST

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