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Full Discussion: how to get the correct reading of diskspace
Operating Systems Linux how to get the correct reading of diskspace Post 302234640 by Annihilannic on Wednesday 10th of September 2008 03:21:45 AM
Old 09-10-2008
Quote:
Originally Posted by jonathan184
So while the process is still running i cleared the log using cat /dev/null > script1.sh then ran rm -rf script1.sh
I presume you meant script1.log, not script1.sh.

Sometimes the cat /dev/null > script1.log (or just >script1.log on its own) is enough. When the next output is written to the file you can end up with a sparse file, where the file size is reported as quite large, but the file only occupies a small space on disk.

The big problem was that you removed the log file with rm, which meant that you could no longer truncate the log.

Here is an example where I create a "log" file, and part way through writing to it, I "flatten" the file. You can see that the file size continues to increase, but the disk usage reported by du drops:

Code:
# while sleep 1 ; do dd if=/dev/zero bs=1048576 count=1 2>/dev/null ; done > /tmp/logfile &
[1]     20489
# ls -l /tmp/logfile
-rw-r--r--   1 root       sys        2097152 Sep 10 07:15 /tmp/logfile
# ls -l /tmp/logfile ; du -ks /tmp/logfile
-rw-r--r--   1 root       sys        8388608 Sep 10 07:15 /tmp/logfile
11264   /tmp/logfile
# ls -l /tmp/logfile ; du -ks /tmp/logfile
-rw-r--r--   1 root       sys        9437184 Sep 10 07:15 /tmp/logfile
11264   /tmp/logfile
# ls -l /tmp/logfile ; du -ks /tmp/logfile
-rw-r--r--   1 root       sys        15728640 Sep 10 07:15 /tmp/logfile
27648   /tmp/logfile
# ls -l /tmp/logfile ; du -k /tmp/logfile
-rw-r--r--   1 root       sys        23068672 Sep 10 07:15 /tmp/logfile
27648   /tmp/logfile
# > /tmp/logfile
# ls -l /tmp/logfile ; du -k /tmp/logfile
-rw-r--r--   1 root       sys        33554432 Sep 10 07:15 /tmp/logfile
3072    /tmp/logfile
# ls -l /tmp/logfile ; du -k /tmp/logfile
-rw-r--r--   1 root       sys        35651584 Sep 10 07:15 /tmp/logfile
11264   /tmp/logfile
# ls -l /tmp/logfile ; du -k /tmp/logfile
-rw-r--r--   1 root       sys        36700160 Sep 10 07:15 /tmp/logfile
11264   /tmp/logfile
# kill %1
#
[1] + Terminated               while sleep 1 ; do dd if=/dev/zero bs=1048576 count=1 2>/dev/null ; done > /tmp/logfile &
#

 

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LEARN ABOUT CENTOS

rename

RENAME(1)							   User Commands							 RENAME(1)

NAME

       rename - rename files

SYNOPSIS

       rename [options] expression replacement file...

DESCRIPTION

       rename will rename the specified files by replacing the first occurrence of expression in their name by replacement.

OPTIONS

       -v, --verbose
	      Give visual feedback which files where renamed, if any.

       -V, --version
	      Display version information and exit.

       -s, --symlink
	      Peform rename on symlink target

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

EXAMPLES

       Given the files foo1, ..., foo9, foo10, ..., foo278, the commands

	      rename foo foo0 foo?
	      rename foo foo0 foo??

       will turn them into foo001, ..., foo009, foo010, ..., foo278.  And

	      rename .htm .html *.htm

       will fix the extension of your html files.

WARNING

       The  renaming  has  no safeguards.  If the user has permission to rewrite file names, the command will perform the action without any ques-
       tions.  For example, the result can be quite drastic when the command is run as root in the /lib directory.  Always make  a  backup  before
       running the command, unless you truly know what you are doing.

SEE ALSO

       mmv(1), mv(1)

AVAILABILITY

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

util-linux							     June 2011								 RENAME(1)
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