08-26-2002
I did a "man mkdir" and I didn't find an answer to these questions.
The mkdir() system call code in the kernel does not directly impose a limit on the length of a filename. However it must talk to the code for filesystem and this will impose a limit. What that limit is depends on the file system. Posix will guarantee at least 14 characters. To be posix compliant, a unix system must allow at least that much. HP-UX still supports the "short filename" option. If you choose, you can make HP-UX enforce a 14 character limit. This is rarely done. The most common limit these days is 255 characters for a filename. And the most common limit for a full path name is 1023.
You probably will find that you have a pathconf() system call that can determine your exact limit. Note that you must give pathconf() a file name because the limits can vary from filesystem to filesystem.
Because a slash is used to separate the components of a pathname, a slash cannot be used inside a component. And binary zero is used to terminate a string. So no binary zeros either. Any other byte value is fair game as far as the kernel is concerned. A filename with an embedded carriage return will cause you nasty problems. And you really will be better off if you limit yourself to printable characters.
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LEARN ABOUT MOJAVE
pathconf
PATHCONF(2) BSD System Calls Manual PATHCONF(2)
NAME
fpathconf, pathconf -- get configurable pathname variables
SYNOPSIS
#include <unistd.h>
long
fpathconf(int fildes, int name);
long
pathconf(const char *path, int name);
DESCRIPTION
The pathconf() and fpathconf() functions provides a method for applications to determine the current value of a configurable system limit or
option variable associated with a pathname or file descriptor.
For pathconf, the path argument is the name of a file or directory. For fpathconf, the fildes argument is an open file descriptor. The name
argument specifies the system variable to be queried. Symbolic constants for each name value are found in the include file <unistd.h>.
The available values are as follows:
_PC_LINK_MAX
The maximum file link count.
_PC_MAX_CANON
The maximum number of bytes in terminal canonical input line.
_PC_MAX_INPUT
The minimum maximum number of bytes for which space is available in a terminal input queue.
_PC_NAME_MAX
The maximum number of bytes in a file name.
_PC_PATH_MAX
The maximum number of bytes in a pathname.
_PC_PIPE_BUF
The maximum number of bytes which will be written atomically to a pipe.
_PC_CHOWN_RESTRICTED
Return 1 if appropriate privileges are required for the chown(2) system call, otherwise 0.
_PC_NO_TRUNC
Return 1 if file names longer than KERN_NAME_MAX are truncated.
_PC_VDISABLE
Returns the terminal character disabling value.
_PC_XATTR_SIZE_BITS
Returns the number of bits used to store maximum extended attribute size in bytes. For example, if the maximum attribute size sup-
ported by a file system is 128K, the value returned will be 18. However a value 18 can mean that the maximum attribute size can be
anywhere from (256KB - 1) to 128KB. As a special case, the resource fork can have much larger size, and some file system specific
extended attributes can have smaller and preset size; for example, Finder Info is always 32 bytes.
_PC_MIN_HOLE_SIZE
If a file system supports the reporting of holes (see lseek(2)), pathconf() and fpathconf() return a positive number that represents
the minimum hole size returned in bytes. The offsets of holes returned will be aligned to this same value. A special value of 1 is
returned if the file system does not specify the minimum hole size but still reports holes.
RETURN VALUES
If the call to pathconf or fpathconf is not successful, -1 is returned and errno is set appropriately. Otherwise, if the variable is associ-
ated with functionality that does not have a limit in the system, -1 is returned and errno is not modified. Otherwise, the current variable
value is returned.
ERRORS
If any of the following conditions occur, the pathconf and fpathconf functions shall return -1 and set errno to the corresponding value.
[EINVAL] The value of the name argument is invalid.
[EINVAL] The implementation does not support an association of the variable name with the associated file.
pathconf() will fail if:
[EACCES] Search permission is denied for a component of the path prefix.
[EIO] An I/O error occurs while reading from or writing to the file system.
[ELOOP] Too many symbolic links are encountered in translating the pathname. This is taken to be indicative of a looping symbolic
link.
[ENAMETOOLONG] A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters.
[ENOENT] The named file does not exist.
[ENOTDIR] A component of the path prefix is not a directory.
fpathconf() will fail if:
[EBADF] fildes is not a valid open file descriptor.
[EIO] An I/O error occurs while reading from or writing to the file system.
SEE ALSO
sysctl(3)
HISTORY
The pathconf and fpathconf functions first appeared in 4.4BSD.
4th Berkeley Distribution June 4, 1993 4th Berkeley Distribution