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Full Discussion: How to copy a binary file while the file is being written to by another process
Top Forums UNIX for Advanced & Expert Users How to copy a binary file while the file is being written to by another process Post 302603953 by Corona688 on Friday 2nd of March 2012 11:10:07 AM
Old 03-02-2012
Reading from a file doesn't disturb anything, at all. The writer doesn't know or care anything else is reading, and the data being written or position it's being written to won't be upset, reset, or altered.

The real worry would be whether you'd get anything sensible by doing so. You could catch the data file in an in-between or invalid state -- a half-written line or some such -- except you've handily told us your application appends, so that earlier records won't be altered; and does so in individual 512-byte blocks.

If your application writes 512 bytes at a time, i.e. one write of 512 bytes instead of 512 writes of 1 byte, you'll never catch the file in a halfway state -- from a user perspective, the file will grow cleanly in 512-byte jumps.

In short, it ought to be safe to simply copy this file. You don't even need to stop the application.
Last edited by Corona688; 03-02-2012 at 12:25 PM..
 

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LEARN ABOUT OSF1

showfdmn

showfdmn(8)						      System Manager's Manual						       showfdmn(8)

NAME

       showfdmn - Display attributes of an AdvFS file domain

SYNOPSIS

       /sbin/showfdmn [-k] domain

OPTIONS

       Displays the total number of blocks and the number of free blocks in terms of 1K blocks.

OPERANDS

       Specifies the name of an existing AdvFS file domain.

DESCRIPTION

       The showfdmn command displays the attributes of a file domain and detailed information about each volume in the file domain.

       The command displays the following file domain attributes: Id

	      A unique number (in hexadecimal format) that identifies a file domain.  Date Created

	      The day, month, and time that a file domain was created.	LogPgs

	      The number of 8-kilobyte pages in the transaction log of the specified file domain.  Version

	      An  internal-use-only version number for the AdvFS on-disk data structures.  This number is not related to the version number of the
	      base operating system.  Domain Name

	      The name of the file domain.

       The command also displays the following volume information: Vol

	      The volume number within the file domain. An L next to the number indicates that the volume contains the transaction log.  512-Blks

	      The size of the volume in 512-byte blocks.  1K-Blks

	      The size of the volume in 1K blocks.  Free

	      The number of blocks in a volume that are available for use.  % Used

	      The percent of volume space that is currently allocated to files or metadata.  Cmode

	      The I/O consolidation mode.  The default mode is on.  Rblks

	      The maximum number of 512-byte blocks read from the volume at one time.  Wblks

	      The maximum number of 512-byte blocks written to the volume at one time.	Vol Name

	      The name of the special device file for the volume.

       For multi-volume file domains, the showfdmn command also displays the total volume size, total number of free blocks, and the total percent
       of volume space currently allocated.

RESTRICTIONS

       A file domain must be active before the showfdmn command can display volume information.  A file domain is active when at least one fileset
       in the file domain is mounted.

EXAMPLES

       The following example displays domain information for the usr_domain file domain: % showfdmn usr_domain

		Id	     Date Created   LogPgs Version Domain Name 2b5361ba.000791be Tue Jan 12 16:26 1999 256	 4 usr_domain

       Vol  512-Blks   Free % Used Cmode Rblks Wblks Vol Name
	1L    820164 351580    57%    on   256	 256 /dev/disk/dsk0d To display information on all file domains on a system, enter  the  following
       sequence of commands: % cd /etc/fdmns % showfdmn *

SEE ALSO

       Commands: chvol(8), mkfdmn(8)

       Files: advfs(4)

																       showfdmn(8)
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