What is the maximum number of files a file system can contain?

Ext4 has a theoretical limit of 4 billion files, which is restricted by the size of inode number it uses to identify each file (ext4 uses 32-bit inode numbers). However, as John says, ext4 allocates inode tables statically, so the actual limit is set when the filesystem is created.

The df command shows you a count of free inodes on your filesystem:

$ df -i

Filesystem        iused     ifree  %iused  Mounted on
/dev/disk0s3   55253386  66810480    45%   /
/dev/disk1s3   55258045  66805821    45%   /Volumes/Clone

Ext4 also supports an unlimited number of sub-directories per directory, though it may default to a limit of 64,000. This is configurable — see the ext4 article at Kernel Newbies.

For more information, see The new ext4 filesystem: current status and future plans from the 2007 Linux Symposium.

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