Linux 101: What’s the SUID permission?

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

Picture: iStockphoto/Elena Kalashnik

Should you’re new to Linux administration, you’ve got most likely already began studying about file permissions. If I mentioned “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, considered one of which I will educate you about proper now. Mentioned permission known as SUID, which stands for Set proprietor Consumer ID. It is a particular permission that applies to scripts or purposes. If the SUID bit is about, when the command is run, it is efficient UID turns into that of the proprietor of the file, as an alternative of the consumer working it. 

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

That is used to supply momentary elevated permissions throughout execution. For instance, if the file being executed was owned by root and has the SUID bit set, regardless of who’s working the script or software, the permissions would at all times (quickly) equal these of root. 

One very easy-to-understand instance of that is when a consumer desires to alter their password they usually concern 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 to write to the required recordsdata to alter the password–hence the SUID bit. 

Should you create a script (owned by the foundation consumer) that wants the SUID bit set, you’d accomplish that like: 

sudo chmod u+s filename 

The place filename is the identify of the script or software. As soon as the SUID bit is about, anytime that software is executed, will probably be executed with quickly 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 it, while you run right into a scenario the place it is clearly needed.

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