LISTXATTR(2)               Linux Programmer's Manual              LISTXATTR(2)

       listxattr, llistxattr, flistxattr - list extended attribute names

       #include <sys/types.h>
       #include <sys/xattr.h>

       ssize_t listxattr(const char *path, char *list, size_t size);
       ssize_t llistxattr(const char *path, char *list, size_t size);
       ssize_t flistxattr(int fd, char *list, size_t size);

       Extended attributes are name:value pairs associated with inodes (files,
       directories, symbolic links, etc.).  They are extensions to the  normal
       attributes  which  are  associated with all inodes in the system (i.e.,
       the stat(2) data).  A complete overview of extended attributes concepts
       can be found in xattr(7).

       listxattr()  retrieves  the list of extended attribute names associated
       with the given path in the filesystem.  The retrieved list is placed in
       list,  a  caller-allocated buffer whose size (in bytes) is specified in
       the argument size.  The list is the set of (null-terminated) names, one
       after  the  other.   Names  of extended attributes to which the calling
       process does not have access may be omitted from the list.  The  length
       of the attribute name list is returned.

       llistxattr()  is identical to listxattr(), except in the case of a sym-
       bolic link, where the list of names of extended  attributes  associated
       with the link itself is retrieved, not the file that it refers to.

       flistxattr()  is  identical to listxattr(), only the open file referred
       to by fd (as returned by open(2)) is interrogated in place of path.

       A single extended attribute name is a null-terminated string.  The name
       includes  a namespace prefix; there may be several, disjoint namespaces
       associated with an individual inode.

       If size is specified as zero, these calls return the  current  size  of
       the  list of extended attribute names (and leave list unchanged).  This
       can be used to determine the size of the buffer that should be supplied
       in  a  subsequent call.  (But, bear in mind that there is a possibility
       that the set of extended attributes may change between the  two  calls,
       so  that it is still necessary to check the return status from the sec-
       ond call.)

       The list of names is returned as an unordered array of  null-terminated
       character strings (attribute names are separated by null bytes ('\0')),
       like this:


       Filesystems that implement POSIX ACLs using extended  attributes  might
       return a list like this:


       On success, a nonnegative number is returned indicating the size of the
       extended attribute name list.  On failure, -1 is returned and errno  is
       set appropriately.

       E2BIG  The  size of the list of extended attribute names is larger than
              the maximum size allowed; the list cannot  be  retrieved.   This
              can  happen  on  filesystems that support an unlimited number of
              extended attributes per file such  as  XFS,  for  example.   See

              Extended  attributes are not supported by the filesystem, or are

       ERANGE The size of the list buffer is too small to hold the result.

       In addition, the errors documented in stat(2) can also occur.

       These system calls have been available on Linux since kernel 2.4; glibc
       support is provided since version 2.3.

       These system calls are Linux-specific.

       As  noted  in xattr(7), the VFS imposes a limit of 64 kB on the size of
       the extended attribute name list returned by listxattr(7).  If the  to-
       tal  size  of attribute names attached to a file exceeds this limit, it
       is no longer possible to retrieve the list of attribute names.

       The following program demonstrates the usage of listxattr()  and  getx-
       attr(2).  For the file whose pathname is provided as a command-line ar-
       gument, it lists all extended file attributes and their values.

       To keep the code simple, the program assumes that  attribute  keys  and
       values  are constant during the execution of the program.  A production
       program should expect and handle changes during execution of  the  pro-
       gram.   For  example,  the  number of bytes required for attribute keys
       might increase between the two calls to  listxattr().   An  application
       could  handle this possibility using a loop that retries the call (per-
       haps up to a predetermined maximum number of attempts)  with  a  larger
       buffer  each time it fails with the error ERANGE.  Calls to getxattr(2)
       could be handled similarly.

       The following output was recorded by first  creating  a  file,  setting
       some extended file attributes, and then listing the attributes with the
       example program.

   Example output
           $ touch /tmp/foo
           $ setfattr -n user.fred -v chocolate /tmp/foo
           $ setfattr -n user.frieda -v bar /tmp/foo
           $ setfattr -n user.empty /tmp/foo
           $ ./listxattr /tmp/foo
           user.fred: chocolate
           user.frieda: bar
           user.empty: <no value>

   Program source (listxattr.c)
       #include <malloc.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <string.h>
       #include <sys/types.h>
       #include <sys/xattr.h>

       main(int argc, char *argv[])
           ssize_t buflen, keylen, vallen;
           char *buf, *key, *val;

           if (argc != 2) {
               fprintf(stderr, "Usage: %s path\n", argv[0]);

            * Determine the length of the buffer needed.
           buflen = listxattr(argv[1], NULL, 0);
           if (buflen == -1) {
           if (buflen == 0) {
               printf("%s has no attributes.\n", argv[1]);

            * Allocate the buffer.
           buf = malloc(buflen);
           if (buf == NULL) {

            * Copy the list of attribute keys to the buffer.
           buflen = listxattr(argv[1], buf, buflen);
           if (buflen == -1) {

            * Loop over the list of zero terminated strings with the
            * attribute keys. Use the remaining buffer length to determine
            * the end of the list.
           key = buf;
           while (buflen > 0) {

                * Output attribute key.
               printf("%s: ", key);

                * Determine length of the value.
               vallen = getxattr(argv[1], key, NULL, 0);
               if (vallen == -1)

               if (vallen > 0) {

                    * Allocate value buffer.
                    * One extra byte is needed to append 0x00.
                   val = malloc(vallen + 1);
                   if (val == NULL) {

                    * Copy value to buffer.
                   vallen = getxattr(argv[1], key, val, vallen);
                   if (vallen == -1)
                   else {
                        * Output attribute value.
                       val[vallen] = 0;
                       printf("%s", val);

               } else if (vallen == 0)
                   printf("<no value>");


                * Forward to next attribute key.
               keylen = strlen(key) + 1;
               buflen -= keylen;
               key += keylen;


       getfattr(1), setfattr(1), getxattr(2), open(2),  removexattr(2),  setx-
       attr(2), stat(2), symlink(7), xattr(7)

       This  page  is  part of release 5.05 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest     version     of     this    page,    can    be    found    at

Linux                             2019-03-06                      LISTXATTR(2)
Man Pages Copyright Respective Owners. Site Copyright (C) 1994 - 2024 Hurricane Electric. All Rights Reserved.