Welcome to your new Linux account!

As a self-appointed system administrator on this machine, I extend my greetings. This machine is still an experimental one, so all sorts of unexpected things can occur, and changes are sure to be made. Be sure to back up your important work on this machine elsewhere. Please bear with this, and don't hesitate to e-mail your suggestions to me at sbratus@ccs.neu.edu.

A few things about the current configuration:

1. What is available?

Please see the list of things already installed
If you need help on a command, type man <command> . Try man ls . To get the manuals in Web format use this Manual Gateway.

2. What special files are there in my account?

The lg directory is for the Looking Glass, the X windows desktop manager. That's where your desktop preferences are stored. Of course, X windows can be used only if you log in from the console in the lab.

The .tcshrc and .login files contain customizations of your shell. Don't edit them unless you are sure. See the next item for tips on command aliases (which can be included into .tcshrc). Currently, they refer to the common files in /etc/dotfiles , which contain a few aliases that make life safer and easier.

The texinputs directory is the default place where TeX and LaTeX will look for your own style and other texinput files. If you need a special TeX package, put it there (it's OK to put into a subdirectory of texinputs ).

3. The shell.

Your login shell (the UNIX command interpreter started as you log in) is, by default, the extended C shell, tcsh. The prompt shows you the host name (handy if you telnet somewhere else) and your current directory. The tilde ~ is the shell's shorthand for your home directory.

3.1 A reminder on paths.

The shell will expand ~ into the full name of your home directory,

      ~  ->  /home/sergey   

while . is expanded into the full name of the current directory.

The command pwd will tell you your current directory.

   $ pwd
      /home/sergey
   $ cd texinputs
   $ pwd
      /home/sergey/texinputs

The command which <command> will tell you where the executable file of command is. For instance,

   $ which emacs
       /usr/bin/emacs

Remember that all paths that start with / are traced from the root, while those that don't start with your current directory.

   
   $ cp  myfile.tex  texinputs/
       copies  myfile.tex  from the current directory into
                          /home/sergey/texinputs/myfile.tex
   $ cp  myfile.tex  /texinputs/ 
       reports error - no directory /texinputs exists
   $ cp  myfile.tex  texinputs   -- directory name without trailing  /  !
       attempts to create file /home/sergey/texinputs  first,
       then, seeing that a directory of that name exists, does the 
       expected.  
   $ cp  ~/myfile.tex  . 
       copies  myfile.tex  from the home directory 
       (that is, /home/sergey/myfile.tex ) into the _current_ directory,
       whatever that might be.  
   $ cp  /home/nick/somfile.tex  ~/mine-now.tex
       steals another user's file and puts it into your home dir under a new
       name.

3.2 Aliases

Most Unix commands are accompanied by options which change their behavior:

   $ ls
       lists the files in current directory, except the files
       whose names that start with  .
   $ ls -a
       shows ALL files
   $ ls -F 
       same as  ls  , but adds  *  to the names of executable files
       and  /  to the names of directories
   $ ls -l
       same as  ls  , but shows owners and sizes of files
   $ rm  *.tex
       removes all files whose names end in  .tex 
   $ rm -i *.tex
       same as above, but asks about removing each file

Suppose you want to run some command always with specific options. Then alias it:

  
    $ alias rm rm -i        -- now rm will work as rm -i 
    $ alias ls ls -F        -- sets ls to be ls -F , always 

Commands aliased like this last until you log out. To load you aliases each time you log in, add them to your .tcshrc file. See /etc/dotfiles/.tcshrc.all for common aliases. To see your current aliases, just type alias <Enter>.

3.3 Useful tools

more myfile -- to look at file page by page
less myfile -- the same, with extra commands, / to search for a word

4. Security

Each file in UNIX has permissions, determining who can read (and copy), write (and delete), and run it (or cd into a directory).

To see permissions on a file, do ls -l .

  
   $ ls -l test.txt
     -rw-r--r--   1 sergey   users         14 Sep  4 18:29 test.txt

This file, test.txt , is owned by sergey, of the group users. Its permissions are -rw-r--r-- , that is:

       -  r  w  -  r  -  -  r  -  -
       ^  user     group    all others 
       |  perm.    perm.    
       |
       +---- it's a regular file

  readable and writable by owner, not executable
  readable, but not writable for anyone in group users
  readable, but not writable for anyone else  

Here are the permissions of a file readable, writable and executable by

    anyone:     -rwxrwxrwx   (very insecure), 
    you alone:  -rwx-----    (others cannot read or copy it, but see below)

If don't want anyone to read your file, do

  
  $ chmod  a-r  test.txt    -- remove reading permissions for all users
  $ chmod  u+r  test.txt    -- give read permission, to you (user) alone

Directories:

     
   drwxr-xr-x   4 sergey   users       1024 Aug 17 00:02 Work

Work is a directory, owned by sergey , of the group users . The leading d in permissions stands for directory. Anyone can cd to this directory and read or copy files from it, but only the user can write and delete files. If you don't want people to view the contents of your directory, do

   
   $ chmod  a-x  Work      -- remove executable permission for all users
   $ chmod  u+x  Work      -- give permission to yourself only

NOTE: If your directory is writable for others, they can delete ANY files in it, even non-readable and non-writable for them !