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Coming from the Windows world, I have found the majority of the folder directory names to be quite intuitive:

  • \Program Files contains files used by programs (surprise!)

  • \Program Files (x86) contains files used by 32-bit programs on 64-bit OSes

  • \Users (formerly Documents and Settings) contains users' files, i.e. documents and settings

    • \Users\USER\Application Data contains application-specific data

    • \Users\USER\Documents contains documents belonging to the user

  • \Windows contains files that belong to the operation of Windows itself

    • \Windows\Fonts stores font files (surprise!)

    • \Windows\Temp is a global temporary directory

et cetera. Even if I had no idea what these folders did, I could guess with good accuracy from their names.

Now I'm taking a good look at Linux, and getting quite confused about how to find my way around the file system.

For example:

  • /bin contains binaries. But so do /sbin, /usr/bin, /usr/sbin, and probably more that I don't know about. Which is which?? What is the difference between them? If I want to make a binary and put it somewhere system-wide, where do I put it?

  • /media contains external media file systems. But so does /mnt. And neither of them contain anything on my system at the moment; everything seems to be in /dev. What's the difference? Where are the other partitions on my hard disk, like the C: and D: that were in Windows?

  • /home contains the user files and settings. That much is intuitive, but then, what is supposed to go into /usr? And how come /root is still separate, even though it's a user with files and settings?

  • /lib contains shared libraries, like DLLs. But so does /usr/lib. What's the difference?

  • What is /etc? Does it really stand for "et cetera", or something else? What kinds of files should go in there -- global or local? Is it a catch-all for things no one knew where to put, or is there a particular use case for it?

  • What are /opt, /proc, and /var? What do they stand for and what are they used for? I haven't seen anything like them in Windows*, and I just can't figure out what they might be for.

If anyone can think of other standard places that might be good to know about, feel free to add it to the question; hopefully this can be a good reference for people like me, who are starting to get familiar with *nix systems.

*OK, that's a lie. I've seen similar things in WinObj, but obviously not on a regular basis. I still don't know what these do on Linux, though.

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Thanks for keeping a good spirit of learning. This topic is often contentious. See my answer to this question for some extra explanations about the fundamental differences between file system structures in Windows vs Linux. –  Caleb Jul 20 '11 at 7:16
    
Don't think of "usr" as the abbreviation of "user" but "Unix System Resources" (even if it's probably a backronym since it did contain users' directories years ago) (linux-training.be/files/books/html/fun/ch09s08.html). –  lgeorget Jun 17 '13 at 13:55
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3 Answers 3

up vote 19 down vote accepted

Linux distributions use the FHS: http://www.pathname.com/fhs/pub/fhs-2.3.html

You can also try man hier.

I'll try to sum up answers your questions off the top of my head, but I strongly suggest that you read through the FHS:

  • /bin is for non-superuser system binaries
  • /sbin is for superuser (root) system binaries
  • /usr/bin & /usr/sbin are for non-critical shared non-superuser or superuser binaries, respectively
  • /mnt is for temporarily mounting a partition
  • /media is for mounting many removable media at once
  • /dev contains your system device files; it's a long story :)
  • The /usr folder, and its subfolders, can be shared with other systems, so that they will have access to the same programs/files installed in one place. Since /usr is typically on a separate filesystem, it doesn't contain binaries that are necessary to bring the system online.
  • /root is separate because it may be necessary to bring the system online without mounting other directories which may be on separate partitions/hard drives/servers
  • Yes, /etc stands for "et cetera". Configuration files for the local system are stored there.
  • /opt is a place where you can install programs that you download/compile. That way you can keep them separate from the rest of the system, with all of the files in one place.
  • /proc contains information about the kernel and running processes
  • /var contains variable size files like logs, mail, webpages, etc.

To access a system, you generally don't need /var, /opt, /usr, /home; some of potentially largest directories on a system.

One of my favorites, which some people don't use, is /srv. It's for data that is being hosted via services like http/ftp/samba. I've see /var used for this a lot, which isn't really its purpose.

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Good overview addressing the specific questions. Note that some distros use /home/users/username for users and /home/services/servicename for what you mention /src being for. I think this works out better in that it's more versatile to partition. You can have it on it's own partition or use the same partition and your user data, which is often what I want to do. –  Caleb Jul 20 '11 at 7:06
    
+1 thanks for the link and the descriptions, those are awesome! :) –  Mehrdad Jul 20 '11 at 7:08
    
/usr should contain files specific to the applications being on the operating system and/or third-party files. It is not intriniscally sharable! Although LSB argues for these being kept in /opt. /usr/share on the other hand can contain files which are sharable across machines of different architectures / OS versions. These are all just conventions though! It's quite possible (though a lot of hard work) to use a completely different structure. There are other conventions though - like Oracle's Optimal Flexible Architecture –  symcbean Jul 20 '11 at 11:23
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Another thing to keep in mind about Unix is the concept that "everything is a file" (or at least looks like one). For example, the stuff in /proc looks like files and directories, but the contents are really created dynamically by the kernel when you access them. This means that you can use the same tools (ls, cat, etc.) to access this information. –  KeithB Jul 20 '11 at 13:32
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@symcbean From the FHS: "... /usr is shareable, read-only data. That means that /usr should be shareable between various FHS-compliant hosts ...". Obviously some files are architecture dependent, and some distributions expect wildly different directory hierarchies. The solution is to do your homework, like a good Admin :) –  bhinesley Jul 20 '11 at 15:46
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I won't answer about what they all mean (others have), but give a little historical context.

First, remember that UNIX is getting close to 40 years old, back in the days of paper tape and 300 baud hard-coded terminals to mainframes (Windows XP system is close to 10 year old). Typing was slow and the need for efficiency in typing outweighed a lot of other considerations. That is the reason for the very short basic commands (i.e. 'ls', 'cat', 'cc', 'dd', etc.). The same was with the directory structures. The thought was that if the command is more than three or four characters then the name was too long.

The /usr directory originally contained user's home directories since most of the commands were in /bin and all the device files were in /dev. Later it was thought to make the primary drive (the root filesystem, '/') small for faster boot times. So other structures like /usr/bin, /usr/include and /usr/lib came about, where /usr was a separate "drive". Much later, it was thought to have user's home directories in /home, yet another drive. And much later than that, to have a /var (short for variable/changable). The /etc directory did mean 'et cetera' since that was the catch-all location of all the system configuration files. The /mnt was used as a temporary place to access a drive (often a backup drive). Directories like /opt, /proc and /media came much much later.

There is a lot that is left out (like /usr/local and /net), but this gives a brief description of why the names are 'less intuitive'.

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+1 I love historical context, it organizes my brain. :) Thanks for taking the time to write this! –  Mehrdad Jul 20 '11 at 7:08
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As already mentioned here, Linux distributions mostly use the FHS, see here for a tutorial-like overview, specially good suited for someone coming from windows.

As a note, Windows directories seem intuitive, superficially. But let me ask you, where do settings for a program belong, as a *.ini file in the programs folder, in Documents and Settings\User (\Application Data or \Local Settings\Application Data), or in the infamous registry? no one knows, not even Microsoft. And so we can go on and on.

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I think the Windows 7 names of the folders are better. i.e. AppData\Roaming vs. AppData\Local -- they describe the kind of data in there. As for configuration information: I think I know where to put it when I see it, but I can't describe it well, I agree. :) –  Mehrdad Jul 20 '11 at 7:12
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