Here the game gets tough. Learn these features, then you'll be ready to say that you `know something about Linux' ;-)
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,
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),
X is either
-, perm is
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/
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 &
-sn are the program switches,
parn are the program parameters.
Now let's see how multitasking works. Programs, running in foreground or background, are called `processes'.
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.
$ progname [-switches] [parameters] [< input] [> output] &  234
This will output a list of currently running processes.
$ ps -ax
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 <PID>
$ 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'.
jobs are identified by the numbers the shell gives them, not by their PID.
(it doesn't always work)
$ bg <job>
$ fg <job>
$ kill <%job>
More information about files.
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
>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;
*' 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
[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;
RENAME) doesn't work for multiple files; that is,
mv *.xxx *.yyywon't work;
mv -ito be warned when a file is going to be overwritten.
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>