If users were able to delete one another's /tmp files, it could wreak havoc on how different applications work. Files are frequently created in /tmp for different user accounts during normal operation of many multi-user systems. The /tmp directory is one of the most common use cases for the sticky bit. In some cases, the sticky bit is more intuitively referred to as a 'restricted deletion flag' or 'restricted deletion bit'. Specifically, when the sticky bit is set, only the user that owns, the user that owns the directory, or the root user can delete files within the directory. Today, the sticky bit restricts who can delete files in a directory on Linux systems. However, that's not what the sticky bit does on modern Linux systems. This had the effect of making programs load faster. In early Unix systems, the sticky bit was used to retain part of a program in swap space after a process exited. One of the more confusing concepts when it comes to Linux file permissions is the sticky bit. rwxr-sr-x 1 root tty 35048 those permissions, we know when we run the wall command, it will run with the privileges of the tty group. The secret2 subdirectory grants no privileges to everyone ls -l /usr/bin/wall The secret1 subdirectory allows read and execute permissions to everyone else. We have two subdirectories in our /topsecretfolder: secret1 and secret2. Let's walk through a simple example using the ls command. If neither your user, nor any of your real or effective groups have access, neither will you. This means it has the same privileges as the associated uid/gid would have. Normally, when a process on a Linux system is started it runs using the uid/gid of whatever user called it. How Commands Work Without Setuid or Setgid To understand why setuid and setgid are needed, let's start with how things work without them. For example, if you want a user to be able to perform a specific task that requires root/superuser privileges, but don't want to give them sudo or root access. Setuid and setgid are a way for users to run an executable with the permissions of the user (setuid) or group (setgid) who owns the file. If you're already comfortable with chmod and chown, let's dive right in! What are Setuid and Setgid? Having a strong understanding of these concepts is critical for passing any Linux certification.īefore diving into the world of umask, setuid, and setgid, we recommend reading up on file permissions, chmod, and chown. We'll review how setuid, setgid, and the sticky bit work and provide a list of common commands to help you get started. Here, we're going to help you do just that. Sticky bit: a bit set on directories that allows only the owner or root can delete files and subdirectoriesīut those are oversimplifications and really comprehending the concepts well enough to pass an exam or use them effectively in the real world requires going a little deeper than that.

Setgid: a bit that makes an executable run with the privileges of the group of the file

Setuid: a bit that makes an executable run with the privileges of the owner of the file It's easy enough to do a web search for the basic definitions: Setuid, setgid, and the sticky bit can be tough for new and aspiring Linux admins to understand.

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