Maximum Number of Files/Directories on Linux

How many files can I put in a directory?

FAT32:

Maximum number of files: 268,173,300
Maximum number of files per directory: 2¹⁶ - 1 (65,535)
Maximum file size: 2 GiB - 1 without LFS, 4 GiB - 1 with

NTFS:

Maximum number of files: 2³² - 1 (4,294,967,295)
Maximum file size
- Implementation: 2⁴⁴ - 2⁶ bytes (16 TiB - 64 KiB)
- Theoretical: 2⁶⁴ - 2⁶ bytes (16 EiB - 64 KiB)
Maximum volume size
- Implementation: 2³² - 1 clusters (256 TiB - 64 KiB)
- Theoretical: 2⁶⁴ - 1 clusters (1 YiB - 64 KiB)

ext2:

Maximum number of files: 10¹⁸
Maximum number of files per directory: ~1.3 × 10²⁰ (performance issues past 10,000)
Maximum file size
- 16 GiB (block size of 1 KiB)
- 256 GiB (block size of 2 KiB)
- 2 TiB (block size of 4 KiB)
- 2 TiB (block size of 8 KiB)
Maximum volume size
- 4 TiB (block size of 1 KiB)
- 8 TiB (block size of 2 KiB)
- 16 TiB (block size of 4 KiB)
- 32 TiB (block size of 8 KiB)

ext3:

Maximum number of files: min(volumeSize / 2¹³, numberOfBlocks)
Maximum file size: same as ext2
Maximum volume size: same as ext2

ext4:

Maximum number of files: 2³² - 1 (4,294,967,295)
Maximum number of files per directory: unlimited
Maximum file size: 2⁴⁴ - 1 bytes (16 TiB - 1)
Maximum volume size: 2⁴⁸ - 1 bytes (256 TiB - 1)

Maximum number of files/directories on Linux?

ext[234] filesystems have a fixed maximum number of inodes; every file or directory requires one inode. You can see the current count and limits with df -i. For example, on a 15GB ext3 filesystem, created with the default settings:

Filesystem           Inodes  IUsed   IFree IUse% Mounted on
/dev/xvda           1933312 134815 1798497    7% /

There's no limit on directories in particular beyond this; keep in mind that every file or directory requires at least one filesystem block (typically 4KB), though, even if it's a directory with only a single item in it.

As you can see, though, 80,000 inodes is unlikely to be a problem. And with the dir_index option (enablable with tune2fs), lookups in large directories aren't too much of a big deal. However, note that many administrative tools (such as ls or rm) can have a hard time dealing with directories with too many files in them. As such, it's recommended to split your files up so that you don't have more than a few hundred to a thousand items in any given directory. An easy way to do this is to hash whatever ID you're using, and use the first few hex digits as intermediate directories.

For example, say you have item ID 12345, and it hashes to 'DEADBEEF02842.......'. You might store your files under /storage/root/d/e/12345. You've now cut the number of files in each directory by 1/256th.

How to obtain the maximum number of subdirectories in a directory from a C program on Linux?

There is no specific limit on the number of files or subdirectories within a given directory. There are limits on the total number of inodes in a file system depending on how the file system was built and (mostly) how much space there is in total in the file system. Each named object requires an inode (but, thanks to hard links, a single inode can have multiple names). Thus, the limit is primarily controlled by the space available in the file system.

There are usually limits on how deep a directory hierarchy can be — that's the POSIX constant {PATH_MAX} defined (or not) in <limits.h>, and the related lower-bounds on the minimum acceptable value for {PATH_MAX} — {_XOPEN_PATH_MAX} (1024) and {_POSIX_PATH_MAX} (256).

You can use the functions fpathconf() and pathconf() to find properties of file systems at run-time. The related function sysconf() handles other configuration properties.

what is the max files per directory in EXT4?

It depends upon the MKFS parameters used during the filesystem creation. Different Linux flavors have different defaults, so it's really impossible to answer your question definitively.

Maximum number of files in one ext3 directory while still getting acceptable performance?

Provided you have a distro that supports the dir_index capability then you can easily have 200,000 files in a single directory. I'd keep it at about 25,000 though, just to be safe. Without dir_index, try to keep it at 5,000.

What is the max number of files that can be kept in a single folder, on Win7/Mac OS X/Ubuntu Filesystems?

In Windows (assuming NTFS): 4,294,967,295 files

In Linux (assuming ext4): also 4 billion files (but it can be less with some custom inode tables)

In Mac OS X (assuming HFS): 2.1 billion

But I have put around 65000 files into a single directory and I have to say just loading the file list can kill an average PC.

Optimal number of files per directory vs number of directories for EXT4

10k files inside a single folder is not a problem on Ext4. It should have the dir_index option enabled by default, which indexes directories content using a btree-like structure to prevent performance issues.

To sum up, unless you create millions of files or use ext2/ext3, you shouldn't have to worry about system or FS performance issues.

That being said, shell tools and commands don't like to be called with a lot of files as parameter ( rm * for example) and may return you an error message saying something like 'too many arguments'. Look at this answer for what happens then.