  From VMS to Linux HOWTO
  By Guido Gonzato,  <guido ``at'' ibogeo.df.unibo.it>, and
  Mike Miller,  <miller5@uiuc.edu>
  v1.1.3, 17 September 1999

  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
     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:
     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:


  o  writing papers with TeX/LaTeX;

  o  programming in Fortran;

  o  doing some graphics;

  o  using Internet services;

  o  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:


  o  Linux and X Window System are properly installed;

  o  there's a system administrator to take care of the technical
     details (please get help from them, not from me ;-) ;

  o  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
  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



  o  Under VMS filenames are in the form filename.extension;version.
     Under Linux, the version number doesn't exist (big limitation, but
     see Section ``Numbered Backups Under Linux''); 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.

  o  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.

  o  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 ``Advanced
  Topics''.


  2.2.  Directories



  o  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.

  o  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.

  o  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
  ``Advanced Topics''.


  2.3.  Programs



  o  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.

  o  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 ``Configuring''). 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.

  o  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;

  o  You can issue several commands on the command line:




  $ command1 ; command2 ; ... ; commandn





  o  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 ``Examples''.


  For multitasking, `queues', and the like, see Section ``Advanced
  Topics''.


  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
  ``Configuring''). 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 ``Advanced Topics''.



  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:


  o  don't press CTRL--Z to issue commands (if you did, you stopped
     emacs. Type fg to resume it);

  o  there's an extensive on-line help. Press CTRL-H ?, or CTRL-H T to
     start a tutorial;

  o  to save a file, press CTRL-X CTRL-S;

  o  to exit, press CTRL-X CTRL-C;

  o  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:


  o  to run a TeX file through TeX, do as usual: tex file.tex;

  o  to turn a .dvi file into a .ps file, type dvips -o filename.ps
     filename.dvi;

  o  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;

  o  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.

  o  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 ``Print Queues''.


  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:


  o  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.

  o  Newsgroups: use tin or slrn, both very intuitive and self-
     explanatory.

  o  ftp: apart from the usual character-based ftp, ask your sysadm to
     install the full-screen ncftp or a graphical ftp client like xftp.

  o  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'.


  o  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 iden-
  tified by its PID.

  o  To see how many processes there are:

  $ ps -ax




  This will output a list of currently running processes.

  o  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'.


  o  To see how many jobs there are:


       $ jobs




  jobs are identified by the numbers the shell gives them, not by their
  PID.

  o  To stop a process running in foreground:


       $ CTRL-C




  (it doesn't always work)

  o  To suspend a process running in foreground:


       $ CTRL-Z




  (ditto)

  o  To send a suspended process into background (it becomes a job):

  $ bg <job>





  o  To bring a job to foreground:


       $ fg <job>





  o  To kill a job:


       $ kill <%job>






  8.3.  Files, Revisited


  More information about files.


  o  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;

  o  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'.  []. 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;

  o  mv (RENAME) doesn't work for multiple files; that is, mv *.xxx
     *.yyy won't work;

  o  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:


  o   .bash_profile or .profile: read by the shell at login time. It's
     like LOGIN.COM;

  o   .bash_logout: read by the shell at logout. It's like LOGOUT.COM;

  o   .bashrc: read by non--login shells.

  o   .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:


  o  first of all, press q to leave the browser;

  o  h gives you extensive help;

  o  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;

  o  /pattern searches forwards for `pattern'; n searches forwards for
     the next match; ?pattern and N search backwards;

  o  m+letter marks current position (e.g. ma); '+letter go to the
     marked position.

  o  :e examines a new file;

  o  !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



  o  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.)

  o  Back-scrolling: pressing SHIFT--PAG UP (the grey key) allows you to
     backscroll a few pages, depending on your PC's video memory.

  o  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.

  o  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.

  o  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 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-)







































