Symptom: when building something, you get an error message such as ... mkdir: cannot create directory `/nix/store/name': Too many links This is usually because you have more than 32,000 subdirectories in /nix/store, as can be seen using ls -l: $ ls -ld /nix/store drwxrwxrwt 32000 nix nix 4620288 Sep 8 15:08 store The ext2 file system is limited to an inode link count of 32,000 (each subdirectory increasing the count by one). Furthermore, the st_nlink field of the stat system call is a 16-bit value. This only happens on very large Nix installations (such as build machines). Quick solution: run the garbage collector. You may want to use the --max-links option. Real solution: put the Nix store on a file system that supports more than 32,000 subdirectories per directory, such as ext4. (This doesn’t solve the st_nlink limit, but ext4 lies to the kernel by reporting a link count of 1 if it exceeds the limit.)