What is chmod 755 Ubuntu?

When you perform chmod 755 filename command you allow everyone to read and execute the file, the owner is allowed to write to the file as well . So, there should be no permission to everyone else other than the owner to write to the file, 755 permission is required.

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What are user permissions?

The authorization given to users that enables them to access specific resources on the network, such as data files, applications, printers and scanners . User permissions also designate the type of access; for example, can data only be viewed (read only) or can they be updated (read/write).

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