From VMS to Linux HOWTO
Guido Gonzato
<guido_``at''_ibogeo.df.unibo.it>
Mike Miller
<miller5@uiuc.edu>
v1.1.4, 22 September 2004
This HOWTO is aimed at all those who have been using VMS and now need or want
to switch to Linux, the free UNIX clone. The transition is made (hopefully)
painless with a step--to--step comparison between commands and available tools.
-------------------------------------------------------------------------------
Table of Contents
1. Introduction
1.1. Why_Linux?
1.2. Comparing_Commands_and_Files
2. Short_Intro
2.1. Files
2.2. Directories
2.3. Programs
2.4. Quick_Tour
3. Editing_Files
4. TeXing
5. Programming
5.1. Fortran
5.2. Using_make
5.3. Shell_Scripts
5.4. C
6. Graphics
7. Mail_and_Internet_Tools
8. Advanced_Topics
8.1. Permissions_and_Ownership
8.2. Multitasking:_Processes_and_Jobs
8.3. Files,_Revisited
8.4. Print_Queues
9. Configuring
10. Useful_Programs
10.1. Browsing_Files:_less
10.2. Numbered_Backups_Under_Linux
10.3. Archiving:_tar_&_gzip
11. Real_Life_Examples
12. Tips_You_Can't_Do_Without
13. Reading_VMS_tapes_from_Linux
13.1. Introduction
13.2. The_Basics
13.3. Some_details
13.4. Comment_on_Block_Size
14. The_End
14.1. Copyright
14.2. Disclaimer
1. Introduction
1.1. Why Linux?
You've heard that UNIX is difficult and balk at the prospect of leaving VMS,
don't you? Don't worry. Linux, one of the finest UNIX clones, is not more
difficult to use than VMS; actually, I find it easier. Although VMS aficionados
may not agree, in many people's opinion Linux is much more powerful and
versatile.
Linux and VMS are both good operating systems and accomplish essentially the
same tasks, but Linux has a few features that make it a good alternative to
VMS. Moreover, Linux is available for PCs while VMS is not, and modern Pentium-
based Linux machines can outperform a VAX. The icing on the cake is the
excellent performance of modern video cards, which turn an X11-based Linux box
into a fast graphic workstation; nearly always, quicker than dedicated
machines.
I imagine you're a university researcher or a student, and that you use VMS for
the following everyday tasks:
* writing papers with TeX/LaTeX;
* programming in Fortran;
* doing some graphics;
* using Internet services;
* et cetera.
In the following sections I'm going to explain to you how to do these tasks
under Linux, exploiting your experience with VMS. Prerequisites:
* Linux and X Window System are properly installed;
* there's a system administrator to take care of the technical details (please
get help from them, not from me ;-) ;
* your shell---the equivalent of DCL---is bash (ask your sysadm).
Please note that this HOWTO is not enough to acquaint you fully with Linux: it
only contains the bare essential to get you started. You should learn more
about Linux to make the most of it (advanced bash features, programming,
regular expressions...). From now on, RMP means `please read the man pages for
further details'. The man pages are the equivalent of the command HELP.
The Linux Documentation Project documents, available on ftp://sunsite.unc.edu:/
pub/Linux/docs/LDP are an important source of information. I suggest that you
read Larry Greenfield's ``Linux User Guide''---it's invaluable for the novice
user.
And now, go ahead.
-------------------------------------------------------------------------------
1.2. Comparing Commands and Files
This table attempts to compare VMS' and Linux' most used commands. Please keep
in mind that the syntax is often very different; for more details, refer to the
following sections.
_____________________________________________________________________________
| |
| VMS Linux Notes |
| ---------------------------------------------------------------------------|
| --- |
| |
| @COMMAND command must be executable |
| COPY file1 file2 cp file1 file2 |
| CREATE/DIR [.dirname] mkdir dirname only one at a time |
| CREATE/DIR [.dir1.dir2] mkdirhier dir/name |
| DELETE filename rm filename |
| DIFF file1 file2 diff -c file1 file2 |
| DIRECTORY ls |
| DIRECTORY [...]file find . -name file |
| DIRECTORY/FULL ls -al |
| EDIT filename vi filename, you won't like it |
| emacs filename, EDT compatible |
| jed filename ditto---my |
| favourite |
| FORTRAN prog.for g77 prog.f, no need to do LINK |
| f77 prog.f, |
| fort77 prog.f |
| HELP command man command must specify |
| `command' |
| info command ditto |
| LATEX file.tex latex file.tex |
| LOGIN.COM .bash_profile, `hidden' file |
| .bashrc ditto |
| LOGOUT.COM .bash_logout ditto |
| MAIL mail, crude |
| elm, much better |
| pine better still |
| mutt ditto |
| PRINT file.ps lpr file.ps |
| PRINT/QUEUE=laser file.ps lpr -Plaser file.ps |
| PHONE user talk user |
| RENAME file1 file2 mv file1 file2 not for multiple |
| files |
| RUN progname progname |
| SEARCH file "pattern" grep pattern file |
| SET DEFAULT [-] cd .. |
| SET DEFAULT [.dir.name] cd dir/name |
| SET HOST hostname telnet hostname, not exactly the |
| same |
| rlogin hostname |
| SET FILE/OWNER_UIC=joe chown joe file completely different |
| SET NOBROADCAST mesg |
| SET PASSWORD passwd |
| SET PROT=(perm) file chmod perm file completely different |
| SET TERMINAL export TERM= different syntax |
| SHOW DEFAULT pwd |
| SHOW DEVICE du, df |
| SHOW ENTRY lpq |
| SHOW PROCESS ps -ax |
| SHOW QUEUE lpq |
| SHOW SYSTEM top |
| SHOW TIME date |
| SHOW USERS w |
| STOP kill |
| STOP/QUEUE kill, for processes |
| lprm for print queues |
| SUBMIT command command & |
| SUBMIT/AFTER=time command at time command |
| TEX file.tex tex file.tex |
| TYPE/PAGE file more file |
| less file much better
|
|_____________________________________________________________________________|
But of course it's not only a matter of different command names. Read on.
-------------------------------------------------------------------------------
2. Short Intro
This is what you absolutely need to know before logging in the first time.
Relax, it's not much.
-------------------------------------------------------------------------------
2.1. Files
* Under VMS filenames are in the form filename.extension;version. Under Linux,
the version number doesn't exist (big limitation, but see Section Section
10.2); the filename has normally a limit of 255 characters and can have as
many dots as you like. Example of filename: This.is_a_FILEname.txt.
* Linux distinguishes between upper case and lower case characters:
FILENAME.txt and filename.txt are two different files; ls is a command, LS is
not.
* A filename starting with a dot is a `hidden' file (that is, it won't normally
show up in dir listings), while filenames ending with a tilde '˜' represent
backup files.
Now, a table to sum up how to translate commands from VMS to Linux:
_______________________________________________________________________
| |
|
VMS Linux |
| ---------------------------------------------------------------------|
| |
| $ COPY file1.txt file2.txt $ cp file1.txt file2.txt |
| $ COPY [.dir]file.txt [] $ cp dir/file.txt . |
| $ COPY [.dir]file.txt [-] $ cp dir/file.txt .. |
| $ DELETE *.dat;* $ rm *dat |
| $ DIFF file1 file2 $ diff -c file1 file2 |
| $ PRINT file $ lpr file |
| $ PRINT/queue=queuename file $ lpr -Pprintername file |
| $ SEARCH *.tex;* "geology" $ grep geology *tex |
|_______________________________________________________________________|
For other examples involving directories, see below; for details about
protections, ownership, and advanced topics, see Section Section_8.
-------------------------------------------------------------------------------
2.2. Directories
* Within the same node and device, directories names under VMS are in the form
[top.dir.subdir]; under Linux, /top/dir/subdir/. On the top of the directory
tree lies the so--called `root directory' called /; underneath there are
other directories like /bin, /usr, /tmp, /etc, and others.
* The directory /home contains the so--called users' `home directories': e.g. /
home/guido, /home/warner, and so on. When a user logs in, they start working
in their home dir; it's the equivalent of SYS$LOGIN. There's a shortcut for
the home directory: the tilde '˜'. So, cd ˜/tmp is the same as, say, cd /
home/guido/tmp.
* Directory names follow the same rules as file names. Furthermore, each
directory has two special entries: one is . and refers to the directory
itself (like []), and .. that refers to the parent directory (like [-]).
And now for some other examples:
_______________________________________________________________________
| |
|
VMS Linux |
| ---------------------------------------------------------------------|
| |
| $ CREATE/DIR [.dirname] $ mkdir dirname |
| $ CREATE/DIR [.dir1.dir2.dir3] $ mkdirhier dir1/dir2/dir3 |
| n/a $ rmdir dirname |
| (if dirname is empty) |
| $ rm -R dirname |
| $ DIRECTORY $ ls |
| $ DIRECTORY [...]file.*;* $ find . -name "file*" |
| $ SET DEF SYS$LOGIN $ cd |
| $ SET DEF [-] $ cd .. |
| $ SET DEF [top.dir.subdir] $ cd /top/dir/subdir |
| $ SET DEF [.dir.subdir] $ cd dir/subdir |
| $ SHOW DEF $ pwd
|
|_______________________________________________________________________|
For protections, ownership, and advanced topics, see Section Section_8.
-------------------------------------------------------------------------------
2.3. Programs
* Commands, compiled programs, and shell scripts (VMS' `command files') don't
have sort of mandatory extensions like .EXE or .COM and can be called
whatever you like. Executable files are marked by an asterisk '*' when you
issue ls -F.
* To run an executable file, just type its name (no RUN PROGRAM.EXE or
@COMMAND). Caveat: it's essential that the file be located in a directory
included in the path of executables, which is a list of directories.
Typically, the path includes dirs like /bin, /usr/bin, /usr/X11R6/bin, and
others. If you write your own programs, put them in a directory you have
included in the path (see how in Section Section_9). As an alternative, you
may run a program specifying its complete path: e.g., /home/guido/data/
myprog; or ./myprog, if the current directory isn't in the path.
* Command switches are obtained with /OPTION= under VMS, and with -switch or --
switch under Linux, where switch is a letter, more letters combined, or a
word. In particular, the switch -R (recursive) of many Linux commands
performs the same action as [...] under VMS;
* You can issue several commands on the command line:
________________________________________
| |
| $ command1 ; command2 ; ... ; commandn|
|________________________________________|
* Most of the flexibility of Linux comes from two features awkwardly
implemented or missing in VMS: I/O redirection and piping. (I have been told
that recent versions of DCL support redirection and piping, but I don't have
that version.) Redirection is a side feature under VMS (remember the switch /
OUTPUT= of many commands), or a fastidious process, like:
________________________________
| |
| $ DEFINE /USER SYS$OUTPUT OUT |
| $ DEFINE /USER SYS$INPUT IN |
| $ RUN PROG |
|________________________________|
which has the simple Linux (UNIX) equivalent:
___________________
| |
| $ prog < in > out|
|___________________|
Piping is not readily available under VMS, but has a key role under UNIX. A
typical example:
_________________________________________________________________________
| |
| $ myprog < datafile | filter_1 | filter_2 >> result.dat 2> errors.log &|
|_________________________________________________________________________|
which means: the program myprog gets its input from the file datafile (via
<), its output is piped (via |) to the program filter_1 that takes it as
input and processes it, the resulting output is piped again to filter_2 for
further processing, the final output is appended (via >>) to the file
result.dat, and error messages are redirected (via 2>) onto the file
errors.log. All this in background (& at the end of the command line). More
about this in Section Section_11.
For multitasking, `queues', and the like, see Section Section_8.
-------------------------------------------------------------------------------
2.4. Quick Tour
Now you are ready to try Linux out. Enter your login name and password exactly
as they are. For example, if your login name and password are john and
My_PassWd, don't type John or my_passwd. Remember, UNIX distinguishes between
capital and small letters.
Once you've logged in, you'll see a prompt; chances are it'll be something like
machinename:$. If you want to change the prompt or make some programs start
automatically, you'll have to edit a `hidden' file called .profile or
.bash_profile (see example in Section Section_9). This is the equivalent of
LOGIN.COM.
Pressing ALT--F1, ALT--F2, ... ALT--F6 switches between `virtual consoles'.
When one VC is busy with a full--screen application, you can flip over to
another and continue to work. Try and log in to another VC.
Now you may want to start X Window System (from now on, X). X is a graphic
environment very similar to DECWindows---actually, the latter derives from the
former. Type the command startx and wait a few seconds; most likely you'll see
an open xterm or equivalent terminal emulator, and possibly a button bar. (It
depends on how your sysadm configured your Linux box.) Click on the desktop
(try both mouse buttons) to see a menu.
While in X, to access the text mode (`console') sessions press CTRL--ALT--F1
... CTRL--ALT--F6. Try it. When in console, go back to X pressing ALT--F7. To
quit X, follow the menu instructions or press CTRL--ALT--BS.
Type the following command to list your home dir contents, including the hidden
files:
__________
| |
| $ ls -al|
|__________|
Press SHIFT--PAG UP to back-scroll. Now get help about the ls command typing:
__________
| |
| $ man ls|
|__________|
pressing 'q' to exit. To end the tour, type exit to quit your session. If now
you want to turn off your PC, press CTRL--ALT--DEL and wait a few seconds
(never switch off the PC while in Linux! You could damage the filesystem.)
If you think you're ready to work, go ahead, but if I were you I'd jump to
Section Section_8.
-------------------------------------------------------------------------------
3. Editing Files
Linux doesn't have EDT, but there are scores of editors available. The only one
that's guaranteed to be included in every UNIX version is vi---forget it, your
sysadm must have installed something better. Probably the most popular editor
is emacs, which can emulate EDT to a certain degree; jed is another editor that
provides EDT emulation.
These two editors are particularly useful for editing program sources, since
they have two features unknown to EDT: syntax hilighting and automatic
indentation. Moreover, you can compile your programs from within the editor
(command ESC-X compile); in case of a syntax error, the cursor will be
positioned on the offending line. I bet that you'll never want to use the true
blue EDT again.
If you have emacs: start it, then type ESC-X edt-emulation-on. Pressing ALT--
X or ESC-X is emacs' way of issuing commands, like EDT's CTRL--Z. From now on,
emacs acts like EDT apart from a few commands. Differences:
* don't press CTRL--Z to issue commands (if you did, you stopped emacs. Type fg
to resume it);
* there's an extensive on-line help. Press CTRL-H ?, or CTRL-H T to start a
tutorial;
* to save a file, press CTRL-X CTRL-S;
* to exit, press CTRL-X CTRL-C;
* to insert a new file in a buffer, press CTRL-X CTRL-F, then CTRL-X B to
switch among buffers.
If you have jed: ask your sysadm to configure jed properly. Emulation is
already on when you start it; use the normal keypad keys, and press CTRL--
H CTRL--H or CTRL-? to get help. Commands are issued in the same way as emacs'.
In addition, there are some handy key bindings missing in the original EDT; key
bindings can also be tailored to your own taste. Ask your sysadm.
In alternative, you may use another editor with a completely different
interface. emacs in native mode is an obvious choice; another popular editor is
joe, which can emulate other editors like emacs itself (being even easier to
use) or the DOS editor. Invoke the editor as jmacs or jstar and press,
respectively, CTRL-X H or CTRL-J to get online help. emacs and jed are much
more powerful than good ol' EDT.
-------------------------------------------------------------------------------
4. TeXing
TeX and LaTeX are identical to their VMS counterparts---only quicker :-), but
the tools to handle the .dvi and .ps files are superior:
* to run a TeX file through TeX, do as usual: tex file.tex;
* to turn a .dvi file into a .ps file, type dvips -o filename.ps filename.dvi;
* to visualize a .dvi file, type within an X session: xdvi filename.dvi &.
Click on the page to magnify. This program is smart: if you edit and run TeX
producing newer versions of the .dvi file, xdvi will update it automatically;
* to visualize a .ps file, type within an X session: ghostview filename.ps &.
Click on the page to magnify. The whole document or selected pages can be
printed. A newer and better program is gv.
* to print the .ps: usually the command lpr mypaper.ps will do, but if the
PostScript printer is called, say, `ps' (ask your sysadm) you'll do: lpr -Pps
mypaper.ps. For more information about print queues, go to Section Section
8.4.
-------------------------------------------------------------------------------
5. Programming
Programming under Linux is much better: there are lots of tools that make
programming easier and quicker. For instance, the drudgery of editing--saving--
exiting--compiling--re-editing can be cut short by using editors like emacs or
jed, as seen above.
-------------------------------------------------------------------------------
5.1. Fortran
Not substantial differences here, but note that at the time of writing the
available (free) compilers are not 100% compatible with VMS'; expect some minor
quirks. (It's actually the VMS compiler which has non-standard extensions.) See
/usr/doc/g77/DOC or /usr/doc/f2c/f2c.ps for details.
Your sysadm has installed a native compiler called g77 (good but, as of version
0.5.21, still not perfectly compatible with DEC Fortran) or possibly the
Fortran to C translator, f2c, and one of the front-ends that make it mimic a
native compiler. In my experience, the package yaf77 is the one that provides
best results.
To compile a Fortran program with g77, edit the source, save it with extension
.f, then do:
________________
| |
| $ g77 myprog.f|
|________________|
which creates by default an executable called a.out (you don't have to link
anything). To give the executable a different name and do some optimisation:
______________________________
| |
| $ g77 -O2 -o myprog myprog.f|
|______________________________|
Beware of optimisations! Ask your sysadm to read the documentation that comes
with the compiler and tell you if there are any problems.
To compile a subroutine:
__________________
| |
| $ g77 -c mysub.f|
|__________________|
This creates a file mysub.o. To link this subroutine to a program, you'll do
__________________________________
| |
| $ g77 -o myprog myprog.f mysub.o|
|__________________________________|
If you have many external subroutines and you want to make a library, do the
following:
____________________________________
| |
| $ cd subroutines/ |
| $ cat *f >mylib.f ; g77 -c mylib.f|
|____________________________________|
This will create mylib.o that you can link to your programs.
Finally, to link an external library called, say, libdummy.so:
__________________________________
| |
| $ g77 -o myprog myprog.f -ldummy|
|__________________________________|
If you have f2c, you only have to use f77 or fort77 instead of g77.
Another useful programming tool is make, described below.
-------------------------------------------------------------------------------
5.2. Using make
The utility make is a tool to handle the compilation of programs that are split
into several source files. The VMS counterparts are MMS and MMK, which have a
different syntax.
Let's suppose you have source files containing your routines, file_1.f,
file_2.f, file_3.f, and a source file of the main program that uses the
routines, myprog.f. If you compile your program manually, whenever you modify
one of the source files you have to figure out which file depends on which,
which file to recompile first, and so on.
Instead of getting mad, you can write a `makefile'. This is a text file
containing the dependencies between your sources: when one is modified, only
the ones that depend on the modified file will be recompiled.
In our example, you'd write a makefile like this:
# This is makefile
# Press the <TAB> key where you see <TAB>!
# It's important: don't use spaces instead.
myprog: myprog.o file_1.o file_2.o file_3.o
<TAB>g77 -o myprog myprog.o file_1.o file_2.o file_3.o
# myprog depends on four object files
myprog.o: myprog.f
<TAB>g77 -c myprog.f
# myprog.o depends on its source file
file_1.o: file_1.f
<TAB>g77 -c file_1.f
# file_1.o depends on its source file
file_2.o: file_2.f file_1.o
<TAB>g77 -c file_2.f file_1.o
# file_2.o depends on its source file and an object file
file_3.o: file_3.f file_2.o
<TAB>g77 -c file_3.f file_2.o
# file_3.o depends on its source file and an object file
# end of makefile.
Save this file as Makefile and type make to compile your program;
alternatively, save it as myprog.mak and type make -f myprog.mak. And of
course, RMP.
-------------------------------------------------------------------------------
5.3. Shell Scripts
Shell scripts are the equivalent of VMS' command files, and allow for very
powerful constructs.
To write a script, all you have to do is write a standard ASCII file containing
the commands, save it, then make it executable with the command chmod +x
<scriptfile>. To execute it, type its name.
Writing scripts under bash is such a vast subject it would require a book by
itself, and I will not delve into the topic any further. I'll just give you a
more-or-less comprehensive and (hopefully) useful example you can extract some
basic rules from.
EXAMPLE: sample.sh
#!/bin/sh
# sample.sh
# I am a comment
# don't change the first line, it must be there
echo "This system is: `uname -a`" # use the output of the command
echo "My name is $0" # built-in variables
echo "You gave me the following $# parameters: "$*
echo "First parameter is: "$1
echo -n "What's your name? " ; read your_name
echo notice the difference: "hi $your_name" # quoting with "
echo notice the difference: 'hi $your_name' # quoting with '
DIRS=0 ; FILES=0
for file in `ls .` ; do
if [ -d ${file} ] ; then # if file is a directory
DIRS=`expr $DIRS + 1` # this means DIRS = DIRS + 1
elif [ -f ${file} ] ; then
FILES=`expr $FILES + 1`
fi
case ${file} in
*.gif|*jpg) echo "${file}: graphic file" ;;
*.txt|*.tex) echo "${file}: text file" ;;
*.c|*.f|*.for) echo "${file}: source file" ;;
*) echo "${file}: generic file" ;;
esac
done
echo "there are ${DIRS} directories and ${FILES} files"
ls | grep "ZxY--!!!WKW"
if [ $? != 0 ] ; then # exit code of last command
echo "ZxY--!!!WKW not found"
fi
echo "enough... type 'man bash' if you want more info."
-------------------------------------------------------------------------------
5.4. C
Linux is an excellent environment to program in C. Taken for granted that you
know C, here are a couple of guidelines. To compile your standard hello.c
you'll use the gcc compiler, which comes as part of Linux and has the same
syntax as g77:
____________________________
| |
| $ gcc -O2 -o hello hello.c|
|____________________________|
To link a library to a program, add the switch -l<libname>. For example, to
link the math library and optimize do
______________________________________
| |
| $ gcc -O2 -o mathprog mathprog.c -lm|
|______________________________________|
(The -l<libname> switch forces gcc to link the library /usr/lib/lib<libname>.a;
so -lm links /usr/lib/libm.a).
When your program is made of several source files, you'll need to use the
utility make described above. Just use gcc and C source files in the makefile.
You can invoke some help about the C functions, that are covered by man pages,
section 3; for example,
________________
| |
| $ man 3 printf|
|________________|
There are lots of libraries available out there; among the first you'll want to
use are ncurses, to handle text mode effects, and svgalib, to do graphics.
-------------------------------------------------------------------------------
6. Graphics
Among the scores of graphic packages available, gnuplot stands out for its
power and ease of use. Go to X and type gnuplot, and have two sample data files
ready: 2D-data.dat (two data per line), and 3D-data.dat (three data per line).
Examples of 2-D graphs:
______________________________________________
| |
| gnuplot> set title "my first graph" |
| gnuplot> plot '2D-data.dat' |
| gnuplot> plot '2D-data.dat' with linespoints|
| gnuplot> plot '2D-data.dat', sin(x) |
| gnuplot> plot [-5:10] '2D-data.dat' |
|______________________________________________|
Example of 3-D graphs (each `row' of X values is followed by a blank line):
___________________________________________________________
| |
| gnuplot> set parametric ; set hidden3d ; set contour |
| gnuplot> splot '3D-data.dat' using 1:2:3 with linespoints|
|___________________________________________________________|
A single-column datafile (e.g., a time series) can also be plotted as a 2-
D graph:
___________________________________________________________
| |
| gnuplot> plot [-5:15] '2D-data-1col.dat' with linespoints|
|___________________________________________________________|
or as a 3-D graph (blank lines in the datafile, as above):
____________________________________________________________
| |
| gnuplot> set noparametric ; set hidden3d |
| gnuplot> splot '3D-data-1col.dat' using 1 with linespoints|
|____________________________________________________________|
To print a graph: if the command to print on your Postscript printer is lpr -
Pps file.ps, issue:
_______________________________
| |
| gnuplot> set term post |
| gnuplot> set out '| lpr -Pps'|
| gnuplot> replot |
|_______________________________|
then type set term x11 to restore. Don't get confused---the last print will
come out only when you quit gnuplot.
For more info, type help or see the examples in directory /usr/lib/gnuplot/
demos/, if you have it.
-------------------------------------------------------------------------------
7. Mail and Internet Tools
Since Internet was born on UNIX machines, you find plenty of nice and easy-to-
use applications under Linux. Here are just some:
* Mail: use elm or pine to handle your email; both programs have on-line help.
For short messages, you could use mail, as in mail -s "hello mate"
user@somewhere < msg.txt. You may like programs like xmail or some such.
* Newsgroups: use tin or slrn, both very intuitive and self-explanatory.
* ftp: apart from the usual character-based ftp, ask your sysadm to install the
full-screen ncftp or a graphical ftp client like xftp.
* WWW: the ubiquitous netscape, or xmosaic, chimera, and arena are graphical
web browsers; a character-based one is lynx, quick and effective.
-------------------------------------------------------------------------------
8. Advanced Topics
Here the game gets tough. Learn these features, then you'll be ready to say
that you `know something about Linux' ;-)
-------------------------------------------------------------------------------
8.1. Permissions and Ownership
Files and directories have permissions (`protections') and ownership, just like
under VMS. If you can't run a program, or can't modify a file, or can't access
a directory, it's because you don't have the permission to do so, and/or
because the file doesn't belong to you. Let's have a look at the following
example:
_________________________________________________________________
| |
| $ ls -l /bin/ls |
| -rwxr-xr-x 1 root bin 27281 Aug 15 1995 /bin/ls*|
|_________________________________________________________________|
The first field shows the permissions of the file ls (owner root, group bin).
There are three types of ownership: owner, group, and others (similar to VMS
owner, group, world), and three types of permissions: read, write (and delete),
and execute.
From left to right, - is the file type (- = ordinary file, d = directory, l =
link, etc); rwx are the permissions for the file owner (read, write, execute);
r-x are the permissions for the group of the file owner (read, execute); r-
x are the permissions for all other users (read, execute).
To change a file's permissions:
___________________________
| |
| $ chmod <whoXperm> <file>|
|___________________________|
where who is u (user, that is owner), g (group), o (other), X is either + or -,
perm is r (read), w (write), or x (execute). Examples:
__________________
| |
| $ chmod u+x file|
|__________________|
this sets the execute permission for the file owner. Shortcut: chmod +x file.
____________________
| |
| $ chmod go-wx file|
|____________________|
this removes write and execute permission for everyone except the owner.
______________________
| |
| $ chmod ugo+rwx file|
|______________________|
this gives everyone read, write, and execute permission.
A shorter way to refer to permissions is with numbers: rwxr-xr-x can be
expressed as 755 (every letter corresponds to a bit: --- is 0, --x is 1, -w- is
2...).
For a directory, rx means that you can cd to that directory, and w means that
you can delete a file in the directory (according to the file's permissions, of
course), or the directory itself. All this is only part of the matter---RMP.
To change a file's owner:
_______________________
| |
| $ chown username file|
|_______________________|
To sum up, a table:
_____________________________________________________________________________
| |
| VMS Linux Notes |
| ---------------------------------------------------------------------------|
| --- |
| |
| SET PROT=(O:RW) file.txt $ chmod u+rw file.txt |
| $ chmod 600 file.txt |
| SET PROT=(O:RWED,W) file $ chmod u+rwx file |
| $ chmod 700 file |
| SET PROT=(O:RWED,W:RE) file $ chmod 755 file |
| SET PROT=(O:RW,G:RW,W) file $ chmod 660 file |
| SET FILE/OWNER_UIC=JOE file $ chown joe file |
| SET DIR/OWNER_UIC=JOE [.dir] $ chown joe dir/ |
|_____________________________________________________________________________|
-------------------------------------------------------------------------------
8.2. Multitasking: Processes and Jobs
More about running programs. There are no `batch queues' under Linux as you're
used to; multitasking is handled very differently. Again, this is what the
typical command line looks like:
_________________________________________________________________
| |
| $ command -s1 -s2 ... -sn par1 par2 ... parn < input > output &|
|_________________________________________________________________|
where -s1, ..., -sn are the program switches, par1, ..., parn are the program
parameters.
Now let's see how multitasking works. Programs, running in foreground or
background, are called `processes'.
* To launch a process in background:
____________________________________________________________
| |
| $ progname [-switches] [parameters] [< input] [> output] &|
| [1] 234 |
|____________________________________________________________|
the shell tells you what the `job number' (the first digit; see below) and
PID (Process IDentifier) of the process are. Each process is identified by
its PID.
* To see how many processes there are:
__________
| |
| $ ps -ax|
|__________|
This will output a list of currently running processes.
* To kill a process:
______________
| |
| $ kill <PID>|
|______________|
You may need to kill a process when you don't know how to quit it the right
way... ;-). Sometimes, a process will only be killed by one of the following:
__________________
| |
| $ kill -15 <PID>|
| $ kill -9 <PID> |
|__________________|
In addition to this, the shell allows you to stop or temporarily suspend a
process, send a process to background, and bring a process from background to
foreground. In this context, processes are called `jobs'.
* To see how many jobs there are:
________
| |
| $ jobs|
|________|
jobs are identified by the numbers the shell gives them, not by their PID.
* To stop a process running in foreground:
__________
| |
| $ CTRL-C|
|__________|
(it doesn't always work)
* To suspend a process running in foreground:
__________
| |
| $ CTRL-Z|
|__________|
(ditto)
* To send a suspended process into background (it becomes a job):
____________
| |
| $ bg <job>|
|____________|
* To bring a job to foreground:
____________
| |
| $ fg <job>|
|____________|
* To kill a job:
_______________
| |
| $ kill <%job>|
|_______________|
-------------------------------------------------------------------------------
8.3. Files, Revisited
More information about files.
* stdin, stdout, stderr: under UNIX, every system component is treated as if it
were a file. Commands and programs get their input from a `file' called stdin
(standard input; usually, the keyboard), put their output on a `file' called
stdout (usually, the screen), and error messages go to a `file' called stderr
(usually, the screen). Using < and > you redirect input and output to a
different file. Moreover, >> appends the output to a file instead of
overwriting it; 2> redirects error messages (stderr); 2>&1 redirects stderr
to stdout, while 1>&2 redirects stdout to stderr. There's a `black hole'
called /dev/null: everything redirected to it disappears;
* wildcards: '*' is almost the same. Usage: * matches all files except the
hidden ones; .* matches all hidden files; *.* matches only those that have a
'.' in the middle, followed by other characters; p*r matches both `peter' and
`piper'; *c* matches both `picked' and `peck'. '%' becomes '?'. There is
another wildcard: the []. Usage: [abc]* matches files starting with a, b, c;
*[I-N,1,2,3] matches files ending with I, J, K, L, M, N, 1, 2, 3;
* mv (RENAME) doesn't work for multiple files; that is, mv *.xxx *.yyy won't
work;
* use cp -i and mv -i to be warned when a file is going to be overwritten.
-------------------------------------------------------------------------------
8.4. Print Queues
Your prints are queued, like under VMS. When you issue a print command, you may
specify a printer name. Example:
__________________________________________________________________
| |
| $ lpr file.txt # this goes to the standard printer |
| $ lpr -Plaser file.ps # this goes to the printer named 'laser'|
|__________________________________________________________________|
To handle the print queues, you use the following commands:
_____________________________________________________________________________
| |
|
VMS Linux |
| ---------------------------------------------------------------------------|
| --- |
| |
| $ PRINT file.ps $ lpr file.ps |
| $ PRINT/QUEUE=laser file.ps $ lpr -Plaser file.ps |
| $ SHOW QUEUE $ lpq |
| $ SHOW QUEUE/QUEUE=laser $ lpq -Plaser |
| $ STOP/QUEUE $ lprm <item>
|
|_____________________________________________________________________________|
-------------------------------------------------------------------------------
9. Configuring
Your sysadm has already provided you with a number of configuration files like
.xinitrc, .bash_profile, .inputrc, and many others. The ones you may want to
edit are:
* .bash_profile or .profile: read by the shell at login time. It's like
LOGIN.COM;
* .bash_logout: read by the shell at logout. It's like LOGOUT.COM;
* .bashrc: read by non--login shells.
* .inputrc: this file customises the key bindings and the behaviour of the
shell.
To give you an example, I'll include my .bash_profile (abridged):
# $HOME/.bash_profile
# don't redefine the path if not necessary
echo $PATH | grep $LOGNAME > /dev/null
if [ $? != 0 ]
then
export PATH="$PATH:/home/$LOGNAME/bin" # add my dir to the PATH
fi
export PS1='LOGNAME:\w\$ '
export PS2='Continued...>'
# aliases
alias bin="cd ~/bin" ; alias cp="cp -i" ; alias d="dir"
alias del="delete" ; alias dir="/bin/ls $LS_OPTIONS --format=vertical"
alias ed="jed" ; alias mv='mv -i'
alias u="cd .." ; alias undel="undelete"
# A few useful functions
inst() # Install a .tar.gz archive in current directory.
{
gzip -dc $1 | tar xvf -
}
cz() # List the contents of a .zip archive.
{
unzip -l $*
}
ctgz() # List the contents of a .tar.gz archive.
{
for file in $* ; do
gzip -dc ${file} | tar tf -
done
}
tgz() # Create a .tgz archive a la zip.
{
name=$1 ; tar -cvf $1 ; shift
tar -rf ${name} $* ; gzip -S .tgz ${name}
}
And this is my .inputrc:
# $HOME/.inputrc
# Last modified: 16 January 1997.
#
# This file is read by bash and defines key bindings to be used by the shell;
# what follows fixes the keys END, HOME, and DELETE, plus accented letters.
# For more information, man readline.
"\e[1~": beginning-of-line
"\e[3~": delete-char
"\e[4~": end-of-line
set bell-style visible
set meta-flag On
set convert-meta Off
set output-meta On
set horizontal-scroll-mode On
set show-all-if-ambiguous On
# (F1 .. F5) are "\e[[A" ... "\e[[E"
"\e[[A": "info "
-------------------------------------------------------------------------------
10. Useful Programs
10.1. Browsing Files: less
You'll use this file browser every day, so I'll give you a couple of tips to
use it at best. First of all, ask your sysadm to configure less so as it can
display not only plain text files, but also compressed files, archives, and so
on.
Like recent versions of TYPE, less lets you browse files in both directions. It
also accepts several commands that are issued pressing a key. The most useful
are:
* first of all, press q to leave the browser;
* h gives you extensive help;
* g to go to beginning of file, G to the end, number+g to go to line `number'
(e.g. 125g), number+% to move to that percentage of the file;
* /pattern searches forwards for `pattern'; n searches forwards for the next
match; ?pattern and N search backwards;
* m+letter marks current position (e.g. ma); '+letter go to the marked
position.
* :e examines a new file;
* !command executes the shell command.
-------------------------------------------------------------------------------
10.2. Numbered Backups Under Linux
Alas, Linux doesn't still support file version numbers, but you overcome this
limitation in two ways. The first is to use RCS, the Revision Control System,
which allows you to keep previous versions of a file. RCS is covered in ``The
RCS MINI-HOWTO'' ( http://sunsite.unc.edu/mdw/HOWTO/mini/RCS.html).
The second way is to use an editor that knows how to deal with numbered
backups; emacs and jed are OK. In emacs, add these lines in your .emacs:
____________________________________________________
| |
| (setq version-control t) |
| (setq kept-new-versions 15) ;;; or any other value|
| (setq kept-old-versions 15) |
| (setq backup-by-copying-when-linked t) |
| (setq backup-by-copying-when-mismatch t) |
|____________________________________________________|
In jed, make sure you have version 0.98.7 or newer; the patch for numbered
backups is available on http://ibogeo.df.unibo.it/guido/slang/backups.sl.
-------------------------------------------------------------------------------
10.3. Archiving: tar & gzip
Under UNIX there are some widely used applications to archive and compress
files. tar is used to make archives, that is collections of files. To make a
new archive:
________________________________________________
| |
| $ tar -cvf <archive_name.tar> <file> [file...]|
|________________________________________________|
To extract files from an archive:
__________________________________________
| |
| $ tar -xpvf <archive_name.tar> [file...]|
|__________________________________________|
To list the contents of an archive:
_____________________________________
| |
| $ tar -tf <archive_name.tar> | less|
|_____________________________________|
Files can be compressed to save disk space using compress, which is obsolete
and shouldn't be used any more, or gzip:
___________________
| |
| $ compress <file>|
| $ gzip <file> |
|___________________|
that creates a compressed file with extension .Z (compress) or .gz (gzip).
These programs don't make archives, but compress files individually. To
decompress, use:
________________________
| |
| $ compress -d <file.Z>|
| $ gzip -d <file.gz> |
|________________________|
RMP.
The unarj, zip and unzip utilities are also available. Files with extension
.tar.gz or .tgz (archived with tar, then compressed with gzip) are very common
in the UNIX world. Here's how to list the contents of a .tar.gz archive:
_________________________________
| |
| $ tar -ztf <file.tar.gz> | less|
|_________________________________|
To extract the files from a .tar.gz archive:
__________________________
| |
| $ tar -zxf <file.tar.gz>|
|__________________________|
-------------------------------------------------------------------------------
11. Real Life Examples
UNIX' core idea is that there are many simple commands that can linked together
via piping and redirection to accomplish even really complex tasks. Have a look
at the following examples. I'll only explain the most complex ones; for the
others, please study the above sections and the man pages.
Problem: ls is too quick and the file names fly away.
Solution:
_____________
| |
| $ ls | less|
|_____________|
Problem: I have a file containing a list of words. I want to sort it in reverse
order and print it.
Solution:
__________________________________
| |
| $ cat myfile.txt | sort -r | lpr|
|__________________________________|
Problem: my data file has some repeated lines! How do I get rid of them?
Solution:
__________________________________________
| |
| $ sort datafile.dat | uniq > newfile.dat|
|__________________________________________|
Problem: I have a file called 'mypaper.txt' or 'mypaper.tex' or some such
somewhere, but I don't remember where I put it. How do I find it?
Solution:
____________________________
| |
| $ find ~ -name "mypaper*" |
|____________________________|
Explanation: find is a very useful command that lists all the files in a
directory tree (starting from ˜ in this case). Its output can be filtered to
meet several criteria, such as -name.
Problem: I have a text file containing the word 'entropy' in this directory, is
there anything like SEARCH?
Solution: yes, try
_______________________
| |
| $ grep -l 'entropy' *|
|_______________________|
Problem: somewhere I have text files containing the word 'entropy', I'd like to
know which and where they are. Under VMS I'd use search entropy [...]*.*;*, but
grep can't recurse subdirectories. Now what?
Solution:
_____________________________________________________
| |
| $ find . -exec grep -l "entropy" {} \; 2> /dev/null|
|_____________________________________________________|
Explanation: find . outputs all the file names starting from the current
directory, -exec grep -l "entropy" is an action to be performed on each file
(represented by {}), \ terminates the command. If you think this syntax is
awful, you're right.
In alternative, write the following script:
#!/bin/sh
# rgrep: recursive grep
if [ $# != 3 ]
then
echo "Usage: rgrep --switches 'pattern' 'directory'"
exit 1
fi
find $3 -name "*" -exec grep $1 $2 {} \; 2> /dev/null
Explanation: grep works like search, and combining it with find we get the best
of both worlds.
Problem: I have a data file that has two header lines, then every line has 'n'
data, not necessarily equally spaced. I want the 2nd and 5th data value of each
line. Shall I write a Fortran program...?
Solution: nope. This is quicker:
________________________________________________________________
| |
| $ awk 'NL > 2 {print $2, "\t", $5}' datafile.dat > newfile.dat|
|________________________________________________________________|
Explanation: the command awk is actually a programming language: for each line
starting from the third in datafile.dat, print out the second and fifth field,
separated by a tab. Learn some awk---it saves a lot of time.
Problem: I've downloaded an FTP site's ls-lR.gz to check its contents. For each
subdirectory, it contains a line that reads "total xxxx", where xxxx is size in
kbytes of the dir contents. I'd like to get the grand total of all these xxxx
values.
Solution:
__________________________________________________________________
| |
| $ zcat ls-lR.gz | awk ' $1 == "total" { i += $2 } END {print i}'|
|__________________________________________________________________|
Explanation: zcat outputs the contents of the .gz file and pipes to awk, whose
man page you're kindly requested to read ;-)
Problem: I've written a Fortran program, myprog, to calculate a parameter from
a data file. I'd like to run it on hundreds of data files and have a list of
the results, but it's a nuisance to ask each time for the file name. Under VMS
I'd write a lengthy command file, and under Linux?
Solution: a very short script. Make your program look for the data file
'mydata.dat' and print the result on the screen (stdout), then write the
following script:
#!/bin/sh
# myprog.sh: run the same command on many different files
# usage: myprog.sh *.dat
for file in $* # for all parameters (e.g. *.dat)
do
# append the file name to result.dat
echo -n "${file}: " >> results.dat
# copy current argument to mydata.dat, run myprog
# and append the output to results.dat
cp ${file} mydata.dat ; myprog >> results.dat
done
Problem: I want to replace `geology' with `geophysics' in all my text files.
Shall I edit them all manually?
Solution: nope. Write this shell script:
#!/bin/sh
# replace $1 with $2 in $*
# usage: replace "old-pattern" "new-pattern" file [file...]
OLD=$1 # first parameter of the script
NEW=$2 # second parameter
shift ; shift # discard the first 2 parameters: the next are the file names
for file in $* # for all files given as parameters
do
# replace every occurrence of OLD with NEW, save on a temporary file
sed "s/$OLD/$NEW/g" ${file} > ${file}.new
# rename the temporary file as the original file
/bin/mv ${file}.new ${file}
done
Problem: I have some data files, I don't know their length and have to remove
their last but one and last but two lines. Er... manually?
Solution: no, of course. Write this script:
#!/bin/sh
# prune.sh: removes n-1th and n-2th lines from files
# usage: prune.sh file [file...]
for file in $* # for every parameter
do
LINES=`wc -l $file | awk '{print $1}'` # number of lines in file
LINES=`expr $LINES - 3` # LINES = LINES - 3
head -n $LINES $file > $file.new # output first LINES lines
tail -n 1 $file >> $file.new # append last line
done
I hope these examples whetted your appetite...
-------------------------------------------------------------------------------
12. Tips You Can't Do Without
* Command completion: pressing <TAB> when issuing a command will complete the
command line for you. Example: you have to type less this_is_a_long_name;
typing in less thi<TAB> will suffice. (If you have other files that start
with the same characters, supply enough characters to resolve any ambiguity.)
* Back-scrolling: pressing SHIFT--PAG UP (the grey key) allows you to
backscroll a few pages, depending on your PC's video memory.
* Resetting the screen: if you happen to more or cat a binary file, your screen
may end up full of garbage. To fix things, blind type reset or this sequence
of characters: echo CTRL-V ESC c RETURN.
* Pasting text: in console, see below; in X, click and drag to select the text
in an xterm window, then click the middle button (or the two buttons together
if you have a two-button mouse) to paste.
* Using the mouse: ask your sysadm to install gpm, a mouse driver for the
console. Click and drag to select text, then right click to paste the
selected text. It works across different VCs.
-------------------------------------------------------------------------------
13. Reading VMS tapes from Linux
(This section was written by Mike Miller)
-------------------------------------------------------------------------------
13.1. Introduction
From time to time you may want to read tapes made on a VMS machine (or tapes
that are made to be readable by VMS and *nix systems). In general, this is
quite easy for DECFILES11A tapes.
Although you may be reading this as part of a Linux mini-HOWTO, I believe that
the information here is applicable to any *nix system - I've done this on
Linux, HP, Sun and DEC *nix systems. The main platform dependences that I know
are device names, which can differ on different systems, and the options to mt
for specifying the device name (for example, mt -f on Linux and mt -t on HPUX
9).
Caveat - I've only tried this with Exabyte 8mm SCSI tape drives. If you've read
other formats (still got those 9-tracks lying around?) let me know and I'll add
a note here.
-------------------------------------------------------------------------------
13.2. The Basics
When reading a tape that has been made with the VMS ``copy'' command (or has at
least been made to look like it was made with copy) all you need to know is
there will be three files on the tape for each actual data file - a header, the
data, and a trailer. The header and trailer are interesting in that they
contain info on the file as it existed under VMS. The data is, well, the data.
Each of these files can be extracted from the tape with the dd command. The
tape can be positioned by skipping around with the mt command.
Example: I've got VMS tape with a series of files on it. The first two were
originally named ce66-2.evt and ce66-3.evt on a VMS system. The tape label is
c66a2.
If I execute these commands:
__________________________________
| |
| > dd if=$TAPE bs=16k of=header1 |
| > dd if=$TAPE bs=16k of=data1 |
| > dd if=$TAPE bs=16k of=trailer1|
| > dd if=$TAPE bs=16k of=header2 |
| > dd if=$TAPE bs=16k of=data2 |
| > dd if=$TAPE bs=16k of=trailer2|
|__________________________________|
I'm left with six files: header1, data1, trailer1, header2, data2 and trailer2.
The syntax here is if="input file", bs="block size" and of="output file". TAPE
is expected to be a variable containing the device name of your tape drive -
for example, /dev/nts0 if you are using the first SCSI tape on Linux.
If you wanted to read the second file, but not the first, you didn't care about
the header, and you wanted to use the original file name, do this:
____________________________________
| |
| > mt -f $TAPE fsf 4 |
| > dd if=$TAPE bs=16k of=ce66-2.evt|
| > mt -f $TAPE fsf 1 |
|____________________________________|
Note the 4 - skip three files for the first file on the tape and one for the
next header. The second mt skips the second file's trailer and positions the
tape at the beginning of the next file - the third VMS header. You can also use
mt to skip backwards (bsf), rewind (rewind) and rewind and unload the tape
(offline, rewoffl).
-------------------------------------------------------------------------------
13.3. Some details
The header and trailer files contain uppercase ASCII data used by VMS to store
file information such as block size. They also contain the file name, which can
be handy if you want to build scripts that automate read files or search for a
particular file. The first header on a tape volume is slightly different than
subsequent headers.
For a file that is the first file on the tape, as in header1 of the above
example, the first four characters will be "VOL1" followed by the volume name.
In the example, header1 starts with "VOL1C66A2". This is followed by a series
of spaces terminated with a numeral. After that is the string "HDR1" which
indicates that this is a file header. The characters immediately following the
HDR1 string are the VMS file name. In the example, this is "HDR1CE66-2.EVT".
The next field is the volume name again.
For files that are not the first file on the tape, the initial VOL1 field is
not present. Other than that the header has the same structure as for the
initial file. Another useful field is the 7th field, which will end with
"DECFILES11A". This must be present on tapes that conform to the DEC Files11A
standard.
__________________________________________________
| |
| field initial header subsequent headers|
| ===== ============= ================== |
| 1 VOL1 + volume name HDR1 + file name |
| 2 3HDR1 + file name volume name |
| 3 volume name |
| |
| 6 ...DECFILES11A |
| 7 ...DECFILES11A |
|__________________________________________________|
For full details on the header and trailer format, see the DEC FILES11A
documentation (on the orange/grey wall - ask your local VMS folks :-).
-------------------------------------------------------------------------------
13.4. Comment on Block Size
In the example, I used a block size of 16k. On a *nix system, there is no block
size associated with a file on disk while, under VMS, each file has a specific
block size. That means that block size doesn't matter too much on the Linux
end... unless it makes it hard to read the tape. If you have difficulty
figuring out the block size and reading a tape, you can try setting the
hardware block size on your tape drive using `mt -f $TAPE setblk 0'. The exact
form of the setblk option (and its availability) may depend on the version of
mt, the tape drive hardware interface and on your particular flavor of *nix.
(Thanks to Wojtek Skulski (<skulski@nsrlc6.nsrl.rochester.edu>) for pointing
out setblk.)
-------------------------------------------------------------------------------
14. The End
14.1. Copyright
Unless otherwise stated, Linux HOWTO documents are copyrighted by their
respective authors. Linux HOWTO documents may be reproduced and distributed in
whole or in part, in any medium physical or electronic, as long as this
copyright notice is retained on all copies. Commercial redistribution is
allowed and encouraged; however, the author would like to be notified of any
such distributions.
All translations, derivative works, or aggregate works incorporating any Linux
HOWTO documents must be covered under this copyright notice. That is, you may
not produce a derivative work from a HOWTO and impose additional restrictions
on its distribution. Exceptions to these rules may be granted under certain
conditions; please contact the Linux HOWTO coordinator at the address given
below.
In short, we wish to promote dissemination of this information through as many
channels as possible. However, we do wish to retain copyright on the HOWTO
documents, and would like to be notified of any plans to redistribute the
HOWTOs.
If you have questions, please contact Tim Bynum, the Linux HOWTO coordinator,
at <linux-howto@sunsite.unc.edu> via email.
-------------------------------------------------------------------------------
14.2. Disclaimer
This work was written following the experience we had at the Settore di
Geofisica of the Universita' di Bologna (Italy), where a VAX 4000 has been
superseded and replaced by Linux-based Pentium PCs. Most of my colleagues are
VMS users, and some of them have switched to Linux.
``From VMS to Linux HOWTO'' was written by Guido Gonzato, <guido_``at''
ibogeo.df.unibo.it> and Mike Miller, <miller5@uiuc.edu> who contributed the
section on reading VMS tapes. Many thanks to my colleagues and friends who
helped me define the needs and habits of the average VMS user, especially to
Dr. Warner Marzocchi.
Please help me improve this HOWTO. I'm not a VMS expert and never will be, so
your suggestions and bug reports are more than welcome.
Enjoy,
Guido =8-)