Processes

A process is an instance of a running program such as the lp program printing a file called file1. Where a command has been entered which specifies a sequence of programs such as:

ls -lR | pr -h"My Program" | lp &

the whole thing is regarded as a single process comprising programs ls, pr and lp running in sequence.

Process Status - System V

The System V version of the ps (process status) command displays information about processes that are currently active within your computer. The straight-forward ps command produces the following listing:

The System V ps command can take certain switches:

The full or detailed (-f) listing produced by System V is:

Process Status - Berkeley

The Berkeley version of ps produces the following basic listing:

The switches applicable to the Berkeley version are:

The detailed (or user-oriented) listing produced by the Berkeley version is:

Note the difference in the meanings of the -u switch between System V and Berkeley. In System V it gives you a listing pertaining to a named user. In Berkeley it invokes the full listing which is listed in user-order rather than process order.

Note that cd is not a process. If you change directory while in a child process, the change is still in effect when you return to the parent process. Real processes cannot affect their parents.

Aborting a Process

To abort the running foreground process: 
Ctrl-C or Del     aborts the process immediately 
                  and returns to shell.
But some programs intercept Ctrl-C because it is a valid command to the program. To abort such programs try: 
Ctrl-\            halts the process, saves its 
                  current memory image in a file 
                  called core, clears the dead body 
                  of the process from memory, then 
                  returns to the shell.

Ctrl-Z            freezes the process intact 
                  and returns to the shell
To kill the frozen (halted) process you must go to another terminal or window, use the ps command to find out the process's PID, then: 
kill 24806        asks Process N° 24806 to terminate itself
kill -9 24806     tells UNIX to forcibly terminate Process 
                  N° 24806
To release a Locked-up Terminal type Ctrl-J then stty sane followed by another Ctrl-J. If Xwindows locks up the whole screen, go to another terminal, use ps to find the PID of the Xwindows process which is called Xgp, then type kill -9 nnnnn, where nnnnn is the PID of Xgp. If you are using Motif or Open Look, the process to kill is the one with :0 (that's colon-zero) after its name. Another way of knowing which process is the GUI is that it is by far the most greedy process alive as regards its consumption of CPU time.

Common Error Messages

No such file or directory 
Arg list too long 
Broken pipe 
Cannot access                 No such file or directory 
Cross-device link             Different file system 
Device or resource busy 
Different file system         [ln your system cannot do soft links]
File exists                   [a file of that name already exists] 
File table overflow           [too many files open at once] 
File too large                [each user is set a maximum file size]
Illegal option                [an invalid switch has been used] 
Insufficient arguments 
I/O error 
Is a directory                [you're treating a directory as a file]
Login incorrect 
No process can be found
No such process 
No such file or directory
No such process 
No more processes             Can't handle any more processes at present 
No space left on device       [disk full etc] 
Not a directory 
Not enough space              [in memory or on disk] 
RE error                      UNIX cannot understand your regular expression 
Read-only file system
Too many links                You've made too many links to a file 
Usage                         You've used incorrect syntax in command 
444 mode                      You don't have permission to delete named file
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