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Full Discussion: SImple command question
Top Forums UNIX for Dummies Questions & Answers SImple command question Post 14949 by Perderabo on Friday 8th of February 2002 08:43:02 AM
Old 02-08-2002
See this post for a explanation of ctime and mtime.

As for creation time, remember that when Ken Thompson wrote unix in 1969 it was revolutionary to have a file system shared by multiple users. The way unix worked back then encouraged people to create a new file and remove the old one if you were updating a file that was accessed by multiple people. Also it was necessary to periodically copy a filesystem to tape and reload the disk to defragment files. These things made a creation date silly.

By the late 70's, unix had more robust filesystems that no longer needed re-orgs and it had file locking system calls. This made creation date a possibility. And indeed HP added it into the first generation of HP-UX. At that time I was a sysadmin of an HP 9000/520 with creation date and an ATT 3B2 without creation date, so I got to see them side by side. Yes, creation date was useful several times a year, but I never really missed it on the 3B2. And creation date expanded both in-core and on-disk inodes by 4 bytes. So it's not like you get it for free. When HP rewrote HP-UX to use the McKusick filesystem, they dropped creation date. No one really complained very loudly.

There is a lot of competition in unix. Any features added to a kernel must pass a cost/benefit test or they will be dropped. The benchmarks enforce this rather strongly. Creation date had its day in court, but I doubt that any unix version still in existence has a creation date.

Microsoft OS's in contrast have little competition and are not written to win benchmarks. That's why they have a poorly thought out selection of features in their kernels.
 

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BACKUP_SETEXP(8)					       AFS Command Reference						  BACKUP_SETEXP(8)

NAME
       backup_setexp - Sets the expiration date for existing dump levels.

SYNOPSIS
       backup setexp -dump <dump level name>+
	   [-expires <expiration date>+] [-localauth]
	   [-cell <cell name>] [-help]

       backup se -d <dump level name>+
	   [-e <expiration date>+]
	   [-l] [-c <cell name>] [-h]

DESCRIPTION
       The backup setexp command sets or changes the expiration date associated with each specified dump level, which must already exist in the
       dump hierarchy.

       Use the -expires argument to associate an expiration date with each dump level. When the Backup System subsequently creates a dump at the
       dump level, it uses the specified value to derive the dump's expiration date, which it records on the label of the tape (or backup data
       file). The Backup System refuses to overwrite a tape until after the latest expiration date of any dump that the tape contains, unless the
       backup labeltape command is used to relabel the tape. If a dump level does not have an expiration date, the Backup System treats dumps
       created at the level as expired as soon as it creates them.

       (Note that the Backup System does not automatically remove a dump's record from the Backup Database when the dump reaches its expiration
       date, but only if the tape that contains the dump is recycled or relabeled. To remove expired and other obsolete dump records, use the
       backup deletedump command.)

       Define either an absolute or relative expiration date:

       o   An absolute expiration date defines the month/day/year (and, optionally, hour and minutes) at which a dump expires. If the expiration
	   date predates the dump creation time, the Backup System immediately treats the dump as expired.

       o   A relative date defines the number of years, months, or days (or a combination of the three) after the dump's creation that it expires.
	   When the Backup System creates a dump at the dump level, it calculates an actual expiration date by adding the relative date to the
	   start time of the dump operation.

       If the command is used to change an existing expiration date associated with a dump level, the new date applies only to dumps created after
       the change. Existing dumps retain the expiration date assigned at the time they were created.

OPTIONS
       -dump <dump level name>+
	   Specifies the full pathname of each dump level to assign the expiration date specified by the -expires argument.

       -expires <expiration date>+
	   Defines the absolute or relative expiration date to associate with each dump level named by the -dump argument. Absolute expiration
	   dates have the following format:

	      [at] {NEVER | <mm>/<dd>/<yyyy> [<hh>:<MM>] }

	   where the optional word at is followed either by the string "NEVER", which indicates that dumps created at the dump level never expire,
	   or by a date value with a required portion (<mm> for month, <dd> for day, and <yyyy> for year) and an optional portion (<hh> for hours
	   and <MM> for minutes).

	   Omit the <hh>:<MM> portion to use the default of midnight (00:00 hours), or provide a value in 24-hour format (for example, "20:30" is
	   8:30 p.m.).	Valid values for the year range from 1970 to 2037; higher values are not valid because the latest possible date in the
	   standard UNIX representation is in February 2038. The command interpreter automatically reduces later dates to the maximum value.

	   Relative expiration dates have the following format:

	      [in] [<years>y] [<months>m] [<days>d]

	   where the optional word in is followed by at least one of a number of years (maximum 9999) followed by the letter "y", a number of
	   months (maximum 12) followed by the letter "m", or a number of days (maximum 31) followed by the letter "d". If providing more than one
	   of the three, list them in the indicated order. If the date that results from adding the relative expiration value to a dump's creation
	   time is later than the latest possible date in the UNIX time representation, the Backup System automatically reduces it to that date.

       -localauth
	   Constructs a server ticket using a key from the local /etc/openafs/server/KeyFile file. The backup command interpreter presents it to
	   the Backup Server, Volume Server and VL Server during mutual authentication. Do not combine this flag with the -cell argument. For more
	   details, see backup(8).

       -cell <cell name>
	   Names the cell in which to run the command. Do not combine this argument with the -localauth flag. For more details, see backup(8).

       -help
	   Prints the online help for this command. All other valid options are ignored.

EXAMPLES
       The following example associates an absolute expiration date of 10:00 p.m. on 31 December 1999 with the dump level "/1998/december":

	  % backup setexp -dump /1998/december -expires at 12/31/1999 22:00

       The following example associates a relative expiration date of 7 days with the two dump levels "/monthly/week1" and "/monthly/week2":

	  % backup setexp -dump /monthly/week1 /monthly/week -expires 7d

PRIVILEGE REQUIRED
       The issuer must be listed in the /etc/openafs/server/UserList file on every machine where the Backup Server is running, or must be logged
       onto a server machine as the local superuser "root" if the -localauth flag is included.

SEE ALSO
       backup(8), backup_adddump(8), backup_deldump(8), backup_listdumps(8)

COPYRIGHT
       IBM Corporation 2000. <http://www.ibm.com/> All Rights Reserved.

       This documentation is covered by the IBM Public License Version 1.0.  It was converted from HTML to POD by software written by Chas
       Williams and Russ Allbery, based on work by Alf Wachsmann and Elizabeth Cassell.

OpenAFS 							    2012-03-26							  BACKUP_SETEXP(8)
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