NAME

       pathname, filename - how pathnames are encoded and interpreted

DESCRIPTION

       Some  system  calls  allow  you  to  pass  a  pathname as a parameter.  When writing code that deals with
       pathnames, there are kernel-space requirements that you must comply  with,  and  user-space  requirements
       that you should comply with.

       The kernel stores pathnames as C strings, that is, sequences of non-null bytes terminated by a null byte.
       There are a few general rules that apply to all pathnames:

       •  The last byte in the sequence needs to be a null byte.

       •  Any other bytes in the sequence need to be non-null bytes.

       •  A 0x2F byte ('/') is always interpreted as a directory separator, and cannot be part of a filename.

       •  A  pathname  can  be  at  most  PATH_MAX bytes long (see limits.h(0p)).  A pathname that's longer than
          PATH_MAX bytes can be split into multiple smaller pathnames and opened piecewise using openat(2).

       •  A filename can be at most a certain number of bytes long.   The  number  is  filesystem-specific  (see
          _PC_NAME_MAX  in  fpathconf(3)).  For maximum portability, programs should be able to handle filenames
          that are as long as the relevant filesystems will allow.  For maximum portability, programs and  users
          should limit the length of their own pathnames to NAME_MAX bytes (see limits.h(0p)).

       Some  filesystems  or  APIs  may  apply  further  restrictions,  such  as requiring shorter filenames, or
       restricting the allowed bytes in a filename.

       For maximum interoperability, programs and users should also limit the characters that they use for their
       own pathnames to characters in the POSIX Portable Filename Character Set.

VERSIONS

       POSIX.1-2024 encourages implementations to disallow creation of filenames containing new-line characters.
       Linux doesn't follow this, and allows using new-line characters.

SEE ALSO

       limits.h(0p), open(2), fpathconf(3), path_resolution(7), mount(8)

Linux man-pages 6.16                               2025-10-29                                        pathname(7)