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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 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 every of which I will educate you about proper now. Mentioned permission is named SUID, which stands for Set proprietor Consumer ID. This can be 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 a substitute of the consumer working it. 

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

That is used to offer momentary 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 (quickly) equal these of root. 

One very easy-to-understand instance of that is when a consumer needs to vary their password and so they concern the sudo passwd command. If the SUID bit wasn’t set on passwd, the command could be run with out elevated privileges, and would not be capable of write to the mandatory recordsdata to vary 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 utility. As soon as the SUID bit is about, anytime that utility is executed, it is going to 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 may not use it each day, you may be glad you already know it, once you run right into a scenario the place it is clearly essential.

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