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Copyright CourseWare Technologies Inc. 1985-1988
Lesson - 4
SOLVING PROBLEMS
P0
Solving Problems|Topics to Learn|4-0|11,48
# Topic
--- -------
1 - Fixing a Non-echoing Terminal
2 - Stopping a Runaway Process
3 - Stopping Unwanted Print Requests
4 - Recovering from a System Crash
5 - Solving Off-line Printer Problems
6 - Solving File System Problems
7 - Solving Other System Problems
8 - Lesson Review
0 - Return to the Main Menu
P1
Solving Problems|Fixing a Non-echoing Terminal|4-1.1|9,48
A non-echoing terminal is any terminal
that does not display characters when they are
entered at the keyboard.
This abnormal condition occurs when a
program which has the "echo" disabled, is
terminated prematurely because of an error
or when the user presses the BREAK key.
P2
Solving Problems|Fixing a Non-echoing Terminal|4-1.2|12,55
To restore a non-echoing terminal to its normal,
echoing condition, follow these steps:
1. Press the CONTROL and the j keys simultaneously
(This is the equivalent of a LINEFEED). Ignore
any messages that are displayed.
2. Enter the command stty sane (this will not be
echoed), then press <CR>. If the terminal
still does not echo characters, then you
probably mistyped stty sane.
2. Press the LINEFEED key and enter the command
reset (this will not be echoed), then press
LINEFEED again. If the terminal still does
not echo characters, then you probably
mistyped the reset command.
P3
Solving Problems|Fixing a Non-echoing Terminal|4-1.3|4,48
If this procedure does not restore the
terminal to normal operation, then you probably
have a runaway process, the solution for which
is explained in the next section.
P4
Solving Problems|Stopping a Runaway Process|4-2.1|9,52
A runaway process is one that cannot be stopped
from the terminal from which it was invoked.
This abnormal condition occurs whenever an
error prevents anything you enter from reaching
the system. Errors like this can occur in a
program where an endless loop occurs so that the
signals "SIGINT" and "SIGQUIT" are ignored.
P5
Solving Problems|Stopping a Runaway Process|4-2.2|14,52
A runaway process may be stopped from another
terminal (or another window) by the owner of the
process or a superuser.
The command syntax for stopping such a process
is:
kill -9 PID
where PID is the process identification number.
Use the ps -ef command to determine the
PID of the runaway process.
Use the ps -aux command to determine the
PID of the runaway process.
P6
Solving Problems|Unwanted Print Requests|4-3.1|14,59
Occasionally a user will send a long file to the
printer that he/she wishes to stop. If the file is still
being processed, i.e., is listed with the ps command, you
may be able to kill the job before it enters the print queue.
Once the job has entered the print queue, you need to
determine the printer identification number of the print
request with the lpstat command and then (as superuser
or as the owner of the process) issue the command to remove
the job from the printer queue (that is, cancel the print
request). The command is:
cancel print-request-id
lprm print-request-id
P7
Solving Problems|Recovering from a System Crash|4-4.1|12,56
A system crash is a sudden disruption in system
operation that prevents any further work on the computer.
System crashes are very rare; however, when they
occur, they result either from some hardware failure or
because of damage to some of the system files.
When a system crash occurs, the system will usually
display a message explaining the cause of the error and
then stop.
P8
Solving Problems|Recovering from a System Crash|4-4.2|15,54
The error that caused a system crash may be
easily correctable, or may be fatal if the computer
has a serious software or hardware malfunction.
Often system errors can be corrected, and the
processing can be brought back to normal simply by
turning the system off and then restarting the
system as described in the System Administrator
tutorial.
Another method for correcting fatal system
problems is to read error dumps when /etc/errdump
is enabled.
Solving Problems|Recovering from a System Crash|4-4.2|10,54
The error that caused a system crash may be
easily correctable, or may be fatal if the computer
has a serious software or hardware malfunction.
Often system errors can be corrected, and the
processing can be brought back to normal simply by
turning the system off and then restarting the
system as described in the System Administrator
tutorial.
P9
Solving Problems|Off-line Printer Problems|4-5.1|3,54
A problem with an off-line printer is usually
suspected when the printer does not produce the
output you expected.
P10
Solving Problems|Off-line Printer Problems|4-5.2|13,54
The first thing that you should check is whether
the line printer is on-line. Other printer hardware
problems include:
1. Paper is jammed in the printer.
2. The printer is set to the serial instead of
the parallel mode or vice-versa.
3. The printer is set to an incorrect character
set. Consult the printer owner's manual for
other possible problems.
If the printer is properly configured, then the
problem is with the spooling software configuration.
P11
Solving Problems|Off-line Printer Problems|4-5.3|9,54
The lpc command is used to control the operation of the
line printer system. It is an interactive program which
lets you do things like:
* enable or disable a printer
* enable or disable a printer's spooling queue
* rearrange the order of jobs in a queue
* check the status of printers, their queues and
their daemons
P12
Solving Problems|Off-line Printer Problems|4-5.4|7,60
If you have a problem with a particular printer:
1. use the lpc program to abort the printer daemon,
2. go to the /usr/spool/lpg directory and remove relevant
spooled files,
3. use the lpc program to start the printer spooling
mechanism again.
P13
Solving Problems|File System Problems|4-6.1|8,48
Most file system errors are detected and
solved automatically by the fsck program.
On the other hand, errors such as write
permission violations, unavailable file system,
and other configuration problems are due to
improper system configuration.
P14
Solving Problems|File System Problems|4-6.2|8,52
Unavailable file systems result from errors
in the script in the /etc/rc file where it fails
to mount the necessary file systems.
An unwritable file system (one which cannot
be written to by anyone) results when a file
system is mounted as a read only file system.
P15
Solving Problems|File System Problems|4-6.3|5,56
Unfortunately, situations do occur when some
critical UNIX system files are lost. Because of the
large size of the UNIX operating system, you may not
know exactly which missing files are causing various
system problems.
P16
Solving Problems|File System Problems|4-6.4|9,56
When you do not know which files to restore or
to modify to bring your UNIX system back to a normal
state, you have two options:
1. call the software support person if you have
one, or
2. reload the system during the lowest system
usage period.
P17
Solving Problems|Solving Other System Problems|4-7.1|12,55
Several other system problems may occur. Your
readiness and understanding are your best insurance.
Restoring free space is necessary when the
system runs out of disk space and prints a message
like:
out of space on /dev/rdisk
You will have look through the specified file system
and remove any unnecessary files to free up more space.
P18
Solving Problems|Solving Other System Problems|4-7.2|12,54
Hidden files, those whose names begin with a
dot (.), or those whose names have control characters
in them, may be removed with:
rm .[a-z]*
or by matching some characters in the name with control
characters, for example:
rm *as*
Be sure you don't remove files like .login!
P19
Solving Problems|Solving Other System Problems|4-7.3|5,58
Lost files or file systems may be restored from
your backups by using the restore, cpio, or tar commands.
If you do not have backups of some critical files, then
you will have to reload the entire UNIX system, hopefully
being able to backup all users' work beforehand.