ISCS Unix Frequently-Asked-Questions (FAQ)

        % tar zxf foobar.tar.gz
	

(a) using zip utility:

you should find sufficient help via

        % zip -help
	

(b) using tar:

        % tar cf foobar.tar <directory or files to be stored>
	

What is normally done after tar is to compress the archive. Various utilities can be used:

        % gzip foobar.tar      OR
        % compress foobar.tar  OR
        % zip foobar.tar
	

• On unix hosts: almost any host should have gzip/gunzip
• Linux: /ftp/nus/Linux/distributions/slackware

(B) BBS/Tin Newsreader-related Qns

At article level (this is where you can see the contents of a message), press the following keys:

'f' to follow up the current article you see

'F' to follow up the thread, but do not quote.

'w' to post and start a new thread in the newsgroup

'r' to respond to the message poster by email

'R' to respond via email without quoting.

B2. When I start up bbs, all the newsgroups were "missing". What happened and what should I do?

The default setting of the tin newsreader is to display only groups that contain at least one article which you have not read. What happened is that there is no new articles in any of the newsgroups that you have not read. That is why no newsgroups are displayed.

If you want all newsgroups with and without unread articles to be displayed, press 'r'.

You can change this default setting by editing an appropriate line in the file tinrc which resides in your .tin subdirectory.

(Pressing 'r' at the newsgroup level toggles whether tin should display all subscribed newsgroups or only those which contain at least one article which you haven't read.
Pressing 'r' at the thread level toggles whether tin should display all threads or only those threads which contains at least one article which you haven't read.)

B3. I have just posted my article/reply, and the message says 'Article posted'. But I can't seem to locate it. Has my posting failed?

NO. This is because there's no instant update of new article postings in tin. You have to come out to the main menu and go back into the newsgroup again to see your article. If you stay in the newsgroup without exiting to the main menu then you'll forever not able to see your own article, or somebody's new followups.

B4. How do I delete/modify an article I posted?

To delete an article you have posted, press 'D' at the article level. There is no shortcut key in tin for you to re-edit your article and post it up again. You can however accomplish the same thing by playing around with the posting headers.

WARNING:

'Kill' in tin is NOT equivalent to deleting your article. DO NOT use the shortcut key for 'kill', Control-K, if you wish to delete your posting, or you will fall into the "Control-K trap".

Some users mistakenly use Control-K to delete their postings in tin, not realizing this is actually the keystroke for accessing the auto-kill menu. (From this menu, users can configure tin to automatically kill articles with specific headers or from specific authors.) As a result, it may happen that the user accidentally set some kill options unknowingly. Subsequently the user discovers that "suddenly there is very few or no articles in the bbs recently " or "How come I cannot see my own posting" (the case when the user's own name is in his own kill-file.)

B6. I have fallen into the "Control-K trap". What should I do?

Delete your kill-file:

        % rm ~/.tin/kill
	

Set the 2 environment variables - NAME and ORGANIZATION:

in bash,

        % export NAME='myname'
        % export ORGANIZATION='my_organization'
        

        % setenv NAME 'myname'
        % setenv ORGANIZATION 'my_organization'
	

(C) File-transfer-related Qns

Most probably, you did not specify binary transfer before getting the file. To do so, type 'bin' at the ftp prompt before you initiate the get. The same thing applies for gifs and other non-text files.

C2. How do I upload/download files via a modem connection?

• kermit: look under the directory /ftp/dist/PC/kermit for a FAQ on installation and usage.
• zmodem:
  • download: sz <filename>
  • upload: rz

(D) C-programming-related Qns

Segmentation fault is caused by using a pointer that is pointing to a memory location that does not belong to the user program (or not allocated to the user program). A common cause of this error is that the programmer forget to allocate the necessary memory. For example, the code below should cause a segmentation fault.

        #include 
        main()
        {
            char *cp;              /* pointer to char type */
            printf("%s\n", cp); /*segmentation fault here! */
        }
        

        #include 
        main()
        {
           char *cp;
           cp = (char *) malloc(5);     /* allocates 5 bytes */
           strcpy(cp, "ABCD");  /* 4 bytes in "ABCD" & 1 byte for '\0' */
           printf("%s\n", cp);
           free(cp);
        }
        

D2. I got a bus error running my program. What does it mean?

The general reason for a bus error is changing a pointer to hold an odd address. If you have any pointers to type char then that might be something to look at. More often it is making a pointer to type char point at some group of int. The compiler will see the int as being something it can use the faster address registers with (address registers must be word-aligned on the SparcServer) but it will see the pointer to type char as something which can be incremented by ones. The first time you increment that char pointer you will get a bus error.

D3. I am finding a bus error when I compile my program on sununx but when I compile it in ibmunx, there isn't one. Why is this so?

One reason as to why it works on one machine and not another is differences in the way the compliers (forced by architecture) have created the executable. On one machine, you got lucky and your program worked. On the other machine, the error appears because of the bounds problem. Or it maybe an alignment problem. Some machines do not allow access to misaligned data, which can cause bus errors. Some compilers have an option like -misalign that can help.

For more questions and answers on C, you may wish to refer to Usenet's C FAQ

(E) Other general/miscellaneuos Qns

To forward mails from another account, such as leonis/cobra (computer center), create a file in the home directory of your leonis/cobra account named .forward. Please note the dot in the filename. This file should contain your DISCS email address. For example, at your leonis prompt, you may do the following:

        % cd ~
        % cat > .forward
        myname@iscs.nus.sg
        <CTRL-D>
        %
    

WARNING:

Do not try to forward your mail from the dept unix machines to the dept vax machines, or the other way round. Your mail will bounce back and forth continuously and never reach you.

Set the environmental variable EDITOR to pico or vi. The application has to read this variable to be effective, most programs do.

in bash,

        % export EDITOR='myeditor'
	

        % setenv EDITOR 'myeditor'
	

        % rm -- -a
        OR  
        % rm ./-a
	

Please approach the ground floor machine room operators. They may help you recover your files if they are not created after the last backup.

E5. How can I convert a postscript file, with .ps extension, to a normal text file?

        % ps2ascii mypsfile.ps

		 or

        % pstotext mypsfile.ps
	

>From tantc@sunA.iscs.nus.sg  Sun Aug  4 14:46:40 1996
From: Tan Tuck Choy 
Message-Id: <199608040646.OAA19251@sunA.iscs.nus.sg>
Subject: Re: nric checksum
Date: Sun, 4 Aug 1996 14:46:37 +0800 (GMT-8)

> 
> hi Aaron,
> 
> remembered a while ago, there was an article posted by you 
> in the bbs, explaining the derivation of NRIC checksum.
> did you save that article?

no, i didn't.

> this is bcos i would like to include it in the faq.
> the faq is currently being maintained by NUSLib, taken
> over from Wai Sum(graduated), a while ago.

the weights corresponding to the 7 digits, from left to right,
are 2,7,6,5,4,3,2.  multiply each weight with its corresponding
digit, and sum up all these products.  divide the sum by 11 to
obtain the remainder.  subtract this remainder from 11 to get
the final value.  the check code corresponds to this final value
is obtained from this table:

  1 2 3 4 5 6 7 8 9 10 11
  A B C D E F G H I  Z  J


you can rephrase the above.

aaron