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Usual file name errors

Most low-level file functions return some kind of error flag if they cannot perform the action you request, for example, if they cannot parse the file name or find the file. However, to discover which error or what kind of error has occurred, you must frequently refer to the system variable errno. This is an integer specifying the most recent error that has occurred. Macros for values of errno are listed below. They are all defined in the GNU C Library.

The word component below refers to part of a full file name. For example, in the file name /home/fred/snozzberry.txt, fred is a component that designates a subdirectory of the directory /home, and snozzberry.txt is the name of the file proper.

Most functions that accept file name arguments can detect the following error conditions. These are known as the usual file name errors. The names of the errors, such as EACCES, are compounded of E for "error" and a term indicating the type of error, such as ACCES for "access".

The program is not permitted to search within one of the directories in the file name.
Either the full file name is too long, or some component is too long. GNU does not limit the overall length of file names, but depending on which file system you are using, the length of component names may be limited. (For example, you may be running GNU/Linux but accessing a Macintosh HFS disk; the names of Macintosh files cannot be longer than 31 characters.)
Either some component of the file name does not exist, or some component is a symbolic link whose target file does not exist.
One of the file name components that is supposed to be a directory is not a directory.
Too many symbolic links had to be followed to find the file. (GNU has a limit on how many symbolic links can be followed at once, as a basic way to detect recursive (looping) links.)

You can display English text for each of these errors with the m conversion specifier of the printf function, as in the following short example.

errno = EACCES;
printf ("errno string (EACCES): %m\n");

This example prints the following string:

errno string (EACCES): Permission denied

See Formatted output conversion specifiers, for more information on the m conversion specifier.