HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. |  |
NAME |LIBRARY |SYNOPSIS |DESCRIPTION |RETURN VALUE |ATTRIBUTES |VERSIONS |STANDARDS |HISTORY |NOTES |BUGS |EXAMPLES |SEE ALSO |COLOPHON | |
ftw(3) Library Functions Manualftw(3)ftw, nftw - file tree walk
Standard C library (libc,-lc)
#include <ftw.h>int nftw(const char *dirpath,typeof(int (const char *fpath, const struct stat *sb,inttypeflag, struct FTW *ftwbuf))*fn,intnopenfd, intflags);[[deprecated]]int ftw(const char *dirpath,typeof(int (const char *fpath, const struct stat *sb,inttypeflag))*fn,intnopenfd); Feature Test Macro Requirements for glibc (seefeature_test_macros(7)):nftw(): _XOPEN_SOURCE >= 500
nftw() walks through the directory tree that is located under the directorydirpath, and callsfn() once for each entry in the tree. By default, directories are handled before the files and subdirectories they contain (preorder traversal). To avoid using up all of the calling process's file descriptors,nopenfd specifies the maximum number of directories thatnftw() will hold open simultaneously. When the search depth exceeds this,nftw() will become slower because directories have to be closed and reopened.nftw() uses at most one file descriptor for each level in the directory tree. For each entry found in the tree,nftw() callsfn() with four arguments:fpath,sb,typeflag, andftwbuf.fpath is the pathname of the entry, and is expressed either as a pathname relative to the calling process's current working directory at the time of the call tonftw(), ifdirpath was expressed as a relative pathname, or as an absolute pathname, ifdirpath was expressed as an absolute pathname.sb is a pointer to thestat structure returned by a call tostat(2) forfpath. Thetypeflag argument passed tofn() is an integer that has one of the following values:FTW_Ffpath is a regular file.FTW_Dfpath is a directory.FTW_DNRfpath is a directory which can't be read.FTW_DPfpath is a directory, andFTW_DEPTHwas specified inflags. (IfFTW_DEPTHwas not specified inflags, then directories will always be visited withtypeflag set toFTW_D.) All of the files and subdirectories withinfpath have been processed.FTW_NSThestat(2) call failed onfpath, which is not a symbolic link. The probable cause for this is that the caller had read permission on the parent directory, so that the filenamefpath could be seen, but did not have execute permission, so that the file could not be reached forstat(2). The contents of the buffer pointed to bysb are undefined.FTW_SLfpath is a symbolic link, andFTW_PHYSwas set inflags.FTW_SLNfpath is a symbolic link pointing to a nonexistent file. (This occurs only ifFTW_PHYSis not set.) In this case thesb argument passed tofn() contains information returned by performinglstat(2) on the "dangling" symbolic link. (But see BUGS.) The fourth argument (ftwbuf) thatnftw() supplies when callingfn() is a pointer to a structure of typeFTW: struct FTW { int base; int level; };base is the offset of the filename (i.e., basename component) in the pathname given infpath.level is the depth offpath in the directory tree, relative to the root of the tree (dirpath, which has depth 0). To stop the tree walk,fn() returns a nonzero value; this value will become the return value ofnftw(). As long asfn() returns 0,nftw() will continue either until it has traversed the entire tree, in which case it will return zero, or until it encounters an error (such as amalloc(3) failure), in which case it will return -1. Becausenftw() uses dynamic data structures, the only safe way to exit out of a tree walk is to return a nonzero value fromfn(). To allow a signal to terminate the walk without causing a memory leak, have the handler set a global flag that is checked byfn().Don't uselongjmp(3) unless the program is going to terminate. Theflags argument ofnftw() is formed by ORing zero or more of the following flags:FTW_ACTIONRETVAL(since glibc 2.3.3) If this glibc-specific flag is set, thennftw() handles the return value fromfn() differently.fn() should return one of the following values:FTW_CONTINUE Instructsnftw() to continue normally.FTW_SKIP_SIBLINGS Iffn() returns this value, then siblings of the current entry will be skipped, and processing continues in the parent.FTW_SKIP_SUBTREE Iffn() is called with an entry that is a directory (typeflag isFTW_D), this return value will prevent objects within that directory from being passed as arguments tofn().nftw() continues processing with the next sibling of the directory.FTW_STOP Causesnftw() to return immediately with the return valueFTW_STOP. Other return values could be associated with new actions in the future;fn() should not return values other than those listed above. The feature test macro_GNU_SOURCEmust be defined (before includingany header files) in order to obtain the definition ofFTW_ACTIONRETVALfrom<ftw.h>.FTW_CHDIR If set, do achdir(2) to each directory before handling its contents. This is useful if the program needs to perform some action in the directory in whichfpath resides. (Specifying this flag has no effect on the pathname that is passed in thefpath argument offn.)FTW_DEPTH If set, do a post-order traversal, that is, callfn() for the directory itselfafter handling the contents of the directory and its subdirectories. (By default, each directory is handledbefore its contents.)FTW_MOUNT If set, stay within the same filesystem (i.e., do not cross mount points).FTW_PHYS If set, do not follow symbolic links. (This is what you want.) If not set, symbolic links are followed, but no file is reported twice. IfFTW_PHYSis not set, butFTW_DEPTHis set, then the functionfn() is never called for a directory that would be a descendant of itself.ftw()ftw() is an older function that offers a subset of the functionality ofnftw(). The notable differences are as follows: •ftw() has noflags argument. It behaves the same as whennftw() is called withflags specified as zero. • The callback function,fn(), is not supplied with a fourth argument. • The range of values that is passed via thetypeflag argument supplied tofn() is smaller: justFTW_F,FTW_D,FTW_DNR,FTW_NS, and (possibly)FTW_SL.These functions return 0 on success, and -1 if an error occurs. Iffn() returns nonzero, then the tree walk is terminated and the value returned byfn() is returned as the result offtw() ornftw(). Ifnftw() is called with theFTW_ACTIONRETVALflag, then the only nonzero value that should be used byfn() to terminate the tree walk isFTW_STOP, and that value is returned as the result ofnftw().
For an explanation of the terms used in this section, seeattributes(7). ┌──────────────────────────────────┬───────────────┬─────────────┐ │Interface│Attribute│Value│ ├──────────────────────────────────┼───────────────┼─────────────┤ │nftw() │ Thread safety │ MT-Safe cwd │ ├──────────────────────────────────┼───────────────┼─────────────┤ │ftw() │ Thread safety │ MT-Safe │ └──────────────────────────────────┴───────────────┴─────────────┘
In some implementations (e.g., glibc),ftw() will never useFTW_SL; on other systemsFTW_SLoccurs only for symbolic links that do not point to an existing file; and again on other systemsftw() will useFTW_SLfor each symbolic link. Iffpath is a symbolic link andstat(2) failed, POSIX.1-2008 states that it is undefined whetherFTW_NSorFTW_SLis passed intypeflag. For predictable results, usenftw().
POSIX.1-2008.
ftw() POSIX.1-2001, SVr4, SUSv1. POSIX.1-2008 marks it as obsolete.nftw() glibc 2.1. POSIX.1-2001, SUSv1.FTW_SLPOSIX.1-2001, SUSv1.
POSIX.1-2008 notes that the results are unspecified iffn does not preserve the current working directory.
According to POSIX.1-2008, when thetypeflag argument passed tofn() containsFTW_SLN, the buffer pointed to bysb should contain information about the dangling symbolic link (obtained by callinglstat(2) on the link). Early glibc versions correctly followed the POSIX specification on this point. However, as a result of a regression introduced in glibc 2.4, the contents of the buffer pointed to bysb were undefined whenFTW_SLNis passed intypeflag. (More precisely, the contents of the buffer were left unchanged in this case.) This regression was eventually fixed in glibc 2.30, so that the glibc implementation (once more) follows the POSIX specification.
The following program traverses the directory tree under the path named in its first command-line argument, or under the current directory if no argument is supplied. It displays various information about each file. The second command-line argument can be used to specify characters that control the value assigned to theflags argument when callingnftw().Program source #define _XOPEN_SOURCE 500 #include <ftw.h> #include <stdint.h> #include <stdio.h> #include <stdlib.h> #include <string.h> static int display_info(const char *fpath, const struct stat *sb, int tflag, struct FTW *ftwbuf) { printf("%-3s %2d ", (tflag == FTW_D) ? "d" : (tflag == FTW_DNR) ? "dnr" : (tflag == FTW_DP) ? "dp" : (tflag == FTW_F) ? "f" : (tflag == FTW_NS) ? "ns" : (tflag == FTW_SL) ? "sl" : (tflag == FTW_SLN) ? "sln" : "???", ftwbuf->level); if (tflag == FTW_NS) printf("-------"); else printf("%7jd", (intmax_t) sb->st_size); printf(" %-40s %d %s\n", fpath, ftwbuf->base, fpath + ftwbuf->base); return 0; /* To tell nftw() to continue */ } int main(int argc, char *argv[]) { int flags = 0; if (argc > 2 && strchr(argv[2], 'd') != NULL) flags |= FTW_DEPTH; if (argc > 2 && strchr(argv[2], 'p') != NULL) flags |= FTW_PHYS; if (nftw((argc < 2) ? "." : argv[1], display_info, 20, flags) == -1) { perror("nftw"); exit(EXIT_FAILURE); } exit(EXIT_SUCCESS); }stat(2),fts(3),readdir(3)
This page is part of theman-pages (Linux kernel and C library user-space interface documentation) project. Information about the project can be found at ⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report for this manual page, see ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩. This page was obtained from the tarball man-pages-6.15.tar.gz fetched from ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on 2025-08-11. If you discover any rendering problems in this HTML version of the page, or you believe there is a better or more up- to-date source for the page, or you have corrections or improvements to the information in this COLOPHON (which isnot part of the original manual page), send a mail to man-pages@man7.orgLinux man-pages 6.15 2025-05-17ftw(3)Pages that refer to this page:fts(3), readdir(3), attributes(7)
HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |