Davlatjon Sh dalisoft

File Magic Numbers

Magic numbers are the first bits of a file which uniquely identify the type of file. This makes programming easier because complicated file structures need not be searched in order to identify the file type.

For example, a jpeg file starts with ffd8 ffe0 0010 4a46 4946 0001 0101 0047 ......JFIF.....G ffd8 shows that it's a JPEG file, and ffe0 identify a JFIF type structure. There is an ascii encoding of "JFIF" which comes after a length code, but that is not necessary in order to identify the file. The first 4 bytes do that uniquely.

This gives an ongoing list of file-type magic numbers.

Image Files

Every so often I have to restore my gpg keys and I'm never sure how best to do it. So, I've spent some time playing around with the various ways to export/import (backup/restore) keys.

Method 1

Backup the public and secret keyrings and trust database

cp ~/.gnupg/pubring.gpg /path/to/backups/
cp ~/.gnupg/secring.gpg /path/to/backups/
cp ~/.gnupg/trustdb.gpg /path/to/backups/

or, instead of backing up trustdb...

	# The command finds the most recent tag that is reachable from a commit.
	# If the tag points to the commit, then only the tag is shown.
	# Otherwise, it suffixes the tag name with the number of additional commits on top of the tagged object
	# and the abbreviated object name of the most recent commit.
	git describe

	# With --abbrev set to 0, the command can be used to find the closest tagname without any suffix:
	git describe --abbrev=0

	# other examples

	--log_gc (Log heap samples on garbage collection for the hp2ps tool.)
	type: bool default: false
	--expose_gc (expose gc extension)
	type: bool default: false
	--max_new_space_size (max size of the new generation (in kBytes))
	type: int default: 0
	--max_old_space_size (max size of the old generation (in Mbytes))
	type: int default: 0
	--max_executable_size (max size of executable memory (in Mbytes))
	type: int default: 0