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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 MOJAVE

blockdev

BLOCKDEV(8)                                                    System Administration                                                   BLOCKDEV(8)

NAME

       blockdev - call block device ioctls from the command line

SYNOPSIS

       blockdev [-q] [-v] command [command...] device [device...]
       blockdev --report [device...]
       blockdev -h|-V

DESCRIPTION

       The utility blockdev allows one to call block device ioctls from the command line.

OPTIONS

       -q     Be quiet.

       -v     Be verbose.

       --report
              Print  a  report  for  the  specified device. It is possible to give multiple devices. If none is given, all devices which appear in
              /proc/partitions are shown. Note that the partition StartSec is in 512-byte sectors.

       -h, --help
              Display help text and exit.

       -V, --version
              Print version and exit.

COMMANDS

       It is possible to give multiple devices and multiple commands.

       --flushbufs
              Flush buffers.

       --getalignoff
              Get alignment offset.

       --getbsz
              Print blocksize in bytes.

       --getdiscardzeroes
              Get discard zeroes support status.

       --getfra
              Get filesystem readahead in 512-byte sectors.

       --getiomin
              Get minimum I/O size.

       --getioopt
              Get optimal I/O size.

       --getmaxsect
              Get max sectors per request

       --getpbsz
              Get physical block (sector) size.

       --getra
              Print readahead (in 512-byte sectors).

       --getro
              Get read-only. Print 1 if the device is read-only, 0 otherwise.

       --getsize64
              Print device size in bytes.

       --getsize
              Print device size (32-bit!) in sectors. Deprecated in favor of the --getsz option.

       --getss
              Print logical sector size in bytes - usually 512.

       --getsz
              Get size in 512-byte sectors.

       --rereadpt
              Reread partition table

       --setbsz bytes
              Set blocksize. Note that the block size is specific to the current file descriptor opening the block device, so the change of  block
              size only persists for as long as blockdev has the device open, and is lost once blockdev exits.

       --setfra sectors
              Set filesystem readahead (same like --setra on 2.6 kernels).

       --setra sectors
              Set readahead (in 512-byte sectors).

       --setro
              Set  read-only.  The currently active access to the device may not be affected by the change. For example filesystem already mounted
              in read-write mode will not be affected. The change applies after remount.

       --setrw
              Set read-write.

AUTHOR

       blockdev was written by Andries E. Brouwer and rewritten by Karel Zak.

AVAILABILITY

       The blockdev command is part of the util-linux package and is available from https://www.kernel.org/pub/linux/utils/util-linux/.

util-linux                                                          August 2010                                                        BLOCKDEV(8)
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