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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, 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/
|
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 |
To see how many processes there are:
$ ps -ax |
To kill a process:
$ 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'.
To see how many jobs there are:
$ jobs |
To stop a process running in foreground:
$ CTRL-C |
To suspend a process running in foreground:
$ CTRL-Z |
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> |
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.
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> |