On this Linux 101, Jack Wallen explains the SUID permission bit.

Picture: iStockphoto/Elena Kalashnik

In case you’re new to Linux administration, you have in all probability already began studying about file permissions. If I stated “drwxrwxr-x,” you’d know what that meant. It is easy: A listing with proprietor and group learn, write, execute permissions, however solely learn and execute permissions for everybody else. 

That is not the be-all, finish all for permissions. There are literally three extra permissions, one in all which I’ll educate you about proper now. Mentioned permission is known as SUID, which stands for Set proprietor Consumer ID. This can be a particular permission that applies to scripts or functions. If the SUID bit is ready, when the command is run, it is efficient UID turns into that of the proprietor of the file, as an alternative of the person working it. 

SEE: Kubernetes safety information (free PDF) (TechRepublic)

That is used to offer short-term elevated permissions throughout execution. For instance, if the file being executed was owned by root and has the SUID bit set, irrespective of who’s working the script or utility, the permissions would at all times (briefly) equal these of root. 

One very easy-to-understand instance of that is when a person desires to alter their password they usually difficulty the sudo passwd command. If the SUID bit wasn’t set on passwd, the command can be run with out elevated privileges, and would not be capable of write to the required recordsdata to alter the password–hence the SUID bit. 

In case you create a script (owned by the foundation person) that wants the SUID bit set, you’d achieve this like: 

sudo chmod u+s filename 

The place filename is the identify of the script or utility. As soon as the SUID bit is ready, anytime that utility is executed, it will likely be executed with briefly elevated privileges. 

And that is the gist of the SUID permission bit. It sounds extra difficult than it truly is. Though you won’t use it day-after-day, you may be glad you recognize it, if you run right into a scenario the place it is clearly mandatory.

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