Recipe: File permissions, ownership and sticky bit

Setting permissions for files
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$ chmod u=rwx g=rw o=r filename

Adding executable permission to the other users
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$ chmod o+x filename

Removing permission from all
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$ chmod a-x filename

Using numbers to denote permissions
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$ chmod 755 filename


Changing the ownership of files
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$ chown user.group filename

Sticky bits 
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$ chmod a+t directory_name

Applying permissions recursively
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$ chmod 777 . -R

Applying ownership recursively
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$ chown user.group . -R

Running an executable as different user
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$ chmod +s executable_file

# chown root.root executable_file 
# chmod +s executable_file
$ ./executable_file