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Test Your Knowledge in Computers #501
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If a piece of code adds two numbers together and stores the result, there should be a comment that explains the process in the source code.
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lock(1) [bsd man page]

LOCK(1) 						      General Commands Manual							   LOCK(1)

lock - reserve a terminal SYNOPSIS
lock [ -p ] [ -t timeout ] DESCRIPTION
Lock requests a password from the user, reads it again for verification and then will normally not relinquish the terminal until the pass- word is repeated. There are two other conditions under which it will terminate: it will timeout after some interval of time and it may be killed by someone with the appropriate permission. The default time limit is 15 minutes, which may be changed with the -t option where timeout is the time limit in minutes. The -p option causes lock to use the user's current password instead of requesting another one. 3rd Berkeley Distribution February 23, 1989 LOCK(1)

Check Out this Related Man Page

SHLOCK(1)						      General Commands Manual							 SHLOCK(1)

shlock - create lock files for use in shell scripts SYNOPSIS
shlock -p pid -f name [ -b ] [ -u ] [ -c ] DESCRIPTION
Shlock tries to create a lock file named name and write the process ID pid into it. If the file already exists, shlock will read the process ID from the file and test to see if the process is currently running. If the process exists, then the file will not be created. Shlock exits with a zero status if it was able to create the lock file, or non-zero if the file refers to currently-active process. OPTIONS
-b Process IDs are normally read and written in ASCII. If the ``-b'' flag is used, then they will be written as a binary int. For compatibility with other systems, the ``-u'' flag is accepted as a synonym for ``-b'' since binary locks are used by many UUCP pack- ages. -c If the ``-c'' flag is used, then shlock will not create a lock file, but will instead use the file to see if the lock is held by another program. If the lock is valid, the program will exit with a non-zero status; if the lock is not valid (i.e., invoking shlock without the flag would have succeeded), then the program will exit with a zero status. EXAMPLES
The following example shows how shlock would be used within a shell script: LOCK=/var/run/innd/LOCK.send trap 'rm -f ${LOCK} ; exit 1' 1 2 3 15 if shlock -p $$ -f ${LOCK} ; then # Do appropriate work else echo Locked by `cat ${LOCK}` fi HISTORY
Written by Rich $alz <> after a description of HDB UUCP locking given by Peter Honeyman. This is revision 1.9, dated 1996/10/29. SHLOCK(1)

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