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Posts Tagged ‘size’

Linux: remove files that got deleted while written – or how to lose track of files eating up your disk space

Just stumbled across why you should not simply delete files such as:

/var/log/syslog
/var/log/kern.log

These files get written permanently, therefore are opened. The application writing to the file has an according file handle, therefore deleting the file using

rm /var/log/syslog
rm /var/log/kern.log

deletes the representation of the data in the file system, not the data itself. As the file handle used by the application writing to these files uses the inode, not the file name, the file continues to exist. Therefore you do not free disk space – but lose track of the files eating up your space, if you don’t recognize the mistake. To recreate the access to the file via the file system simply recreate the files and restore their ownership:

touch /var/log/syslog
chown syslog:adm /var/log/syslog
touch /var/log/kern.log
chown syslog:adm /var/log/kern.log

You should see the files in the file system again then. If they stay empty (and you did not free any disk size), try:

reload rsyslog

Then you should see the log growing again – and your disk will finally be less occupied.

Categories: Linux Tags: , , , , ,

convertconditional: convert an image if it fulfills certain conditions

August 28, 2013 Leave a comment

Recently I needed a script to batch convert only those images amongst a large amount of images which fulfil certain criteria, namely of being exactly of a stated size. The script is based on ImageMagick’s convert and basically takes an arbitrary amount of convert parameters. I personally use this script to automatically reduce size and quality of photos taken with a specific camera in order to reduce their hard disk space coverage.

The script

#! /usr/bin/python
#
# convertconditional: Convert an image if it fulfills certain conditions, e.g. is of a certain size. Requires ImageMagick's convert.
# Rainhard Findling 2013/08
#
# example to convert all *JPG within the current directory with are of certain size to a reduced size and quality:
# find . -iname "*JPG" -exec ./convertconditional {} -filtersize 3888x2592 -convertparams "-resize 3500x3000 +repage -quality 80" \;
#
import argparse # check http://docs.python.org/2/howto/argparse.html for help
import subprocess
import sys
# specify arguments
parser = argparse.ArgumentParser()
parser.add_argument('inputfile', help='path to the file that will be converted.')
parser.add_argument('-convertparams', required=True, help='parameters handed to the convert command used internally, e.g. resize, repage, reduce quality etc. Example: "-resize 300x200 +replage -quality 92"')
parser.add_argument('-filtersize', help='only convert if original image is of this size, stated as WIDTHxHEIGHT, e.g. 3500x3200.')
parser.add_argument('-o', '--outputfile', help='path to where the converted image will be stored. if not specified, the original file will be overwritten.')
parser.add_argument('-v','--verbose',help='print verbose output.',action='store_true')
args = parser.parse_args()
# make sure we can process names with spaces
args.inputfile = '"' + args.inputfile + '"'
# check for correct arguments
if not args.outputfile:
args.outputfile = args.inputfile
if args.filtersize:
filter_x = int(args.filtersize.split('x')[0])
filter_y = int(args.filtersize.split('x')[1])
if args.verbose:
print 'inputfile=' + args.inputfile
print 'outputfile=' + args.outputfile
if args.filtersize:
print 'resizing only', str(filter_x) + 'x' + str(filter_y), 'images.'
print 'convertparams=' + args.convertparams
# get size of image
imagesize = subprocess.check_output(["identify -format '%wx%h' '" + args.inputfile + "'"],
stderr=subprocess.STDOUT,
shell=True)
imagesize_x = int(imagesize.split('x')[0])
imagesize_y = int(imagesize.split('x')[1])
# condition: filter for images of certain size
if args.filtersize:
if args.verbose:
print 'size of', args.inputfile, 'is', str(imagesize_x) + "x" + str(imagesize_y)
# check filter criteria
if not imagesize_x == filter_x or not imagesize_y == filter_y:
print 'leaving out ' + args.inputfile + ' as it is of size ' +  str(imagesize_x) + "x" + str(imagesize_y) + " (required: " + args.filtersize + ")"
sys.exit(0)
# passed all conditions: convert image
print 'converting ' + args.inputfile + ' (size: ' +  str(imagesize_x) + "x" + str(imagesize_y) + ')'
# convert image
command="convert '" + args.inputfile + "' " + args.convertparams + " '" + args.outputfile + "'"
if args.verbose:
print 'command:', command
imagesize = subprocess.check_output([command],
stderr=subprocess.STDOUT,
shell=True)

The script is written in Python, so all you need to do is save it (e.g. in a file called “convertconditional”) and make it executable:

chmod +x convertconditional

Then you can either call it with stating it’s path (e.g. “./convertconditional [parameters]”), or add it to your systems PATH to call it from everyhwere.

Script execution

In order to convert input.jpg to output.jpg, you can try

convertconditional input.jpg -filtersize 3888x2592 -convertparams "-resize 3500x3000 +repage -quality 85" -o output.jpg
  • -filtersize optional filtering: only convert the image  in case it is exactly of the stated size
  • -convertparams states parameters which should be handed to ImageMagick’s convert
  • -o states where to store the converted image (original image gets overwritten if omitted)

In case you want to conditionally convert multiple files (as with my usecase) you can combine convertconditional with find and overwrite the original files:

find . -iname "*JPG" -exec convertconditional {} -filtersize 3888x2592 -convertparams "-resize 3800x +repage -quality 85" \;