I encountered an option for chmod:
chmod 777 /tyr/....
What is 777 for?
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The world, the file's group, and the file's owner can read, write, and execute the file. The
777 specifies that using octal notation.
For further reading - http://en.wikipedia.org/wiki/File_system_permissions#Octal_notation
The octal permission 777 is equivalent to the symbolic permission
ugo=rwx or as you would see it using
rwxrwxrwx 1 user group 25500 2010-08-01 06:44 filename
Usually, you don't want the world (Other) to be able to write to a file.
For example, if a file is writeable by Other and executable by all (ugo+x) then some malicious user could change the file and it might have dire consequences the next time it's run.
Usually, for executables, 755 is sufficient. For other files, 644 is usually plenty, but sometimes they need to be group writeable (664) or readonly (444) or for the most privacy (400 or 600).