A filesystem is a way to organize and store computer files with their data.

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383
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What is the purpose of the lost+found folder in Linux and Unix?

There is a folder at the root of Linux and Unix operating systems called /lost+found/ What is it for? Under what circumstances would I interact with it? How would I interact with it?
215
votes
5answers
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/usr/bin vs /usr/local/bin on Linux

Why are there so many places to put a binary in Linux? There are atleast these five: /bin/ /sbin/ /usr/bin/ /usr/local/bin/ /usr/local/sbin/ And on my office box, I do not have write permissions ...
91
votes
7answers
32k views

Why are hard links to directories not allowed in UNIX/Linux?

I read in text books that Unix/Linux doesn't allow hard links to directories but does allow soft links. Is it because, when we have cycles and if we create hard links, and after some time we delete ...
78
votes
12answers
7k views

Why is Linux's filesystem designed as a single directory tree?

Can anyone explain why Linux is designed as a single directory tree? Whereas in Windows we can have multiple drives like C:\, and D:\, there is a single root in Unix. Any specific reason there?
73
votes
3answers
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What happens when I run the command cat /proc/cpuinfo?

What happens when I write cat /proc/cpuinfo. Is that a named pipe (or something else) to the OS which reads the CPU info on the fly and generate that text each time I call it?
70
votes
1answer
4k views

Why are there so many different ways to measure disk usage?

When I sum up the sizes of my files, I get one figure. If I run du, I get another figure. If I run du on all the files on my partition, it doesn't match what df claims is used. Why are there so many ...
67
votes
6answers
58k views

What is a Superblock, Inode, Dentry and a File?

From the article Anatomy of the Linux file system by M. Tim Jones, I read that Linux views all the file systems from the perspective of a common set of objects and these objects are superblock, inode, ...
66
votes
5answers
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Find where inodes are being used

So I received a warning from our monitoring system on one of our boxes that the number of free inodes on a filesystem was getting low. df -i output shows this: Filesystem Inodes IUsed ...
64
votes
5answers
46k views

Can I configure my Linux system for more aggressive file system caching?

I am neither concerned about RAM usage (as I've got enough) nor about losing data in case of an accidental shut-down (as my power is backed, the system is reliable and the data are not critical). But ...
61
votes
3answers
3k views

Why does '/' have an '..' entry?

This just baffles me. Why does the root directory contain a reference to a parent directory? bob@bob:/$ ls -a . build home lib32 mnt .rpmdb sys vmlinuz .. cdrom ...
57
votes
4answers
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Reserved space for root on a filesystem - why?

I understand that by default, newly created filesystems will be created with 5% of the space allocated for root. I also know you can change the defined space with: tune2fs -m 1 /dev/sdXY What I'm ...
55
votes
1answer
51k views

How do I find on which physical device a folder is located?

Specifically: I did sudo mkdir /work, and would like to verify it indeed sits on my harddrive and not mapped to some other drive. How do I check where this folder is physically located?
53
votes
4answers
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How to get the complete and exact list of mounted filesystems in Linux?

I usually use mount to check which filesystems are mounted. I also know there is some connection between mount and /etc/mtab but I'm not sure about the details. After reading How to check if /proc/ is ...
50
votes
8answers
6k views

On Unix systems, why do we have to explicitly `open()` and `close()` files to be able to `read()` or `write()` them?

Why do open() and close() exist in the Unix filesystem design? Couldn't the OS just detect the first time read() or write() was called and do whatever open() would normally do?
48
votes
7answers
4k views

How are file types known if not from file suffix?

I would like to know how file types are known if filenames don't have suffixes. For example, a file named myfile could be binary or text to start with, how does the system know if the file is binary ...
47
votes
1answer
103k views

How to determine the filesystem of an unmounted device? [duplicate]

Possible Duplicate: Find filesystem of a partition from a script How to show the filesystem type via the terminal? I'm looking for a command that yields the filesystem type as mount would ...
46
votes
9answers
52k views

Mount Google Drive in Linux?

Now that Google Drive is available, how do we mount it to a Linux filesystem? Similar solutions exist for Amazon S3 and Rackspace Cloud Files.
45
votes
3answers
16k views

What is the difference between procfs and sysfs?

What is the difference between procfs and sysfs? Why are they made as file systems? As I understand it, proc is just something to store the immediate info regarding the processes running in the ...
44
votes
5answers
9k views

Why do hard links exist?

I know what hard links are, but why would I use them? What is the utility of a hard link?
44
votes
5answers
20k views

How can I create a /dev/null-like “blackhole” directory?

I would like to create a "/dev/null" directory (or a "blackhole" directory) such that any files written to it are not really written, but just disappear. I have an application that writes out large ...
43
votes
1answer
31k views

What is a bind mount?

What is a “bind mount”? How do I make one? What is it good for? I've been told to use a bind mount for something, but I don't understand what it is or how to use it.
43
votes
5answers
74k views

Script to monitor folder for new files?

How do I detect new files in a folder with a bash script? I would like to process the files as soon as they are created in the folder. Is this possible to do so or do I have to schedule a script with ...
42
votes
2answers
90k views

timestamp, modification time, and created time of a file

I just know that ls -t and ls -f give different sorting of files and subdirectories under a directory. What are the differences between timestamp, modification time, and created time of a file? How ...
42
votes
4answers
53k views

How does the sticky bit work?

SUID The sticky bit applied to executable programs flagging the system to keep an image of the program in memory after the program finished running. But I don't know that what it's stored in ...
41
votes
2answers
2k views

Why is '.' a hard link in Unix?

I've seen many explanations for why the link count for an empty directory in Unix based OSes is 2 instead of 1. They all say that it's because of the '.' directory, which every directory has pointing ...
38
votes
2answers
19k views

What is this new /run filesystem?

I just ran df -h a minute ago and noticed a filesystem has been added that I'm not familiar with. Does anyone know why /run exists? Is this something that's been added by the kernel? By Arch Linux? ...
37
votes
3answers
5k views

Is an ISO image file a filesystem in its own right?

I am trying to understand what the relationship a xxx.iso file has to the other aspects of a block device, e.g. partitions and a file system. It's common for people to describe accessing or making a ...
36
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7answers
2k views

ZFS under Linux, does it work?

Could I get ZFS to work properly in Linux? Are there any caveats / limitations?
33
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2answers
35k views

how can I recursively delete empty directories in my home directory? [duplicate]

Possible Duplicate: How to remove all empty directories in a subtree? I create directories very often, scattered over my home directory, and I find it very hard to locate and delete them. ...
33
votes
2answers
104k views

How to show the filesystem type via the terminal? [duplicate]

Possible Duplicate: How to tell what type of filesystem you’re on? Find filesystem of an unmounted partition from a script How can I quickly check the filesystem of the partition? Can I ...
33
votes
3answers
14k views

Birth is empty on ext4

I was just reading up on the Birth section of stat and it appears ext4 should support it, but even a file I just created leaves it empty. ~ % touch test ...
32
votes
3answers
6k views

Why are text files 4kB?

For some reason, when I make a text file on OS X, it's always at least 4kB, unless it's blank. Why is this? Could there be 4,000 bytes of metadata about 1 byte of plain text?
32
votes
5answers
35k views

Clear unused space with zeros (ext3,ext4)

How to clear unused space with zeros ? (ext3,ext4) I'm looking for something smarter than cat /dev/zero > /mnt/X/big_zero ; sync; rm /mnt/X/big_zero Like FSArchiver is looking for "used space" ...
32
votes
3answers
30k views

How can I edit symlinks?

My basic understanding of a symlink is as a special file, a file that contains a string path to another file. The kernel's VFS abstracts a lot of that away but is there any reason why symlinks seem to ...
31
votes
4answers
2k views

Append huge files to each other without copying them

There are 5 huge files ( file1, file2, .. file5) about 10G each and extremely low free space left on the disk and I need to concatenate all this files into one. There is no need to keep original ...
31
votes
5answers
52k views

How can I increase the number of inodes in an ext4 filesystem?

I had a problem (new to me) last week. I have a ext4 (Fedora 15) filesystem. The application that runs on the server suddenly stopped. I couldn't find the problem at first look. df showed 50% ...
29
votes
1answer
10k views

Purpose of /dev/zero?

I tried to cat /dev/zero, and it didn't seem to do anything. I googled /dev/zero, and it says it's basically a blank file with infinite size. Is cat printing an infinite number of non-existent ...
28
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2answers
21k views

What happens when you delete a hard link?

If you do rm myFile where myFile is a hard link, what happens?
28
votes
3answers
8k views

Where are filenames stored on a filesystem?

Where are filenames stored on a filesystem? It's not in inode or with the actual file content since we have hard link that two filenames can point to the same inode.
28
votes
8answers
15k views

Is there a file search engine like “Everything” in Linux?

On Windows there a nice file search engine called Everything, which is (unlike find) very fast and (unlike locate) always returns up to date results. AFAIK it works by filling a database from the ...
28
votes
4answers
80k views

Recovering ext4 superblocks

Recently, my external hard drive enclosure failed (the hard drive itself powers up in another enclosure). However, as a result, it appears its EXT4 file system is corrupt. The drive has a single ...
27
votes
1answer
2k views

Why does “ls *” take so much longer than “ls”?

I have a couple of files in a directory: $ ls | wc -l 9376 Can anybody explain why there is such a huge time difference in using ls * and ls? $ time ls > /dev/null real 0m0.118s user ...
27
votes
3answers
21k views

File system compatible with all OSes?

I use Linux and Mac OS X on a regular basis, and sometimes I have to use Windows. I need to use a flash drive on all three, and I need a filesystem that will work well on all of them. None of the ...
27
votes
2answers
7k views

understanding “mount” as a concept in the OS

I want to understand what mounting is. It is used in different contexts and situations and I can't find resources which: Describe the mount concept Explain the actions taken by the ...
26
votes
5answers
8k views

How to tell which file is original if hard link is created

For example, I have a file myold_file. Then I use ln to create a hard link as mylink: ln myold_file mylink Then, even by using ls -a, I cannot tell which is the old one. Is there anyway to tell?
26
votes
2answers
8k views

I made a mistake last night, which deleted 1800GB of my File-Server unintentionally

I ran this command yesterday, I thought on a test machine, but it was a File-Server connected through SSH. sudo rm -rf /tmp/* !(lost+found) My terminal emulator is Konsole. My system is Debian 7. ...
26
votes
5answers
2k views

How does Linux differentiate between real and unexisting (eg: device) files?

This is a rather low-level question, and I understand that it might not be the best place to ask. But, it seemed more appropriate than any other SE site, so here goes. I know that on the Linux ...
26
votes
2answers
6k views

Where do the files go if you mount a drive to a folder that already contains files?

I just accidentally mounted a new drive to a folder that already contained files. I don't care about them and have them somewhere else, but that folder appears empty now. I'm curious what happened ...
26
votes
2answers
15k views

What mount points exist on a typical Linux system?

I have 2 questions. During Linux installation we specify memory space for 2 mount points - root and swap. Are there any other mount points created without the users notice? Is this statement ...
26
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1answer
5k views

What do the device files in /dev actually do?

(Not a duplicate of Understanding /dev and its subdirs and files) I was browsing around my filesystem and for the first time I took a second to analyze my /dev directory. I was surprised by the ...