NAME

       listmount - get a list of mount ID's

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <linux/mount.h>  /* Definition of struct mnt_id_req constants */
       #include <unistd.h>

       int syscall(size_t n;
                   SYS_listmount, struct mnt_id_req *req,
                   uint64_t mnt_ids[n], size_t n,
                   unsigned long flags);

       #include <linux/mount.h>

       struct mnt_id_req {
           __u32  size;    /* sizeof(struct mnt_id_req) */
           __u64  mnt_id;  /* The parent mnt_id being searched */
           __u64  param;   /* The next mnt_id we want to find */
       };

       Note: glibc provides no wrapper for listmount(), necessitating the use of syscall(2).

DESCRIPTION

       To access the mounts in your namespace, you must have CAP_SYS_ADMIN in the user namespace.

       This  function  returns a list of mount IDs under the req.mnt_id.  This is meant to be used in conjuction
       with statmount(2) in order to provide a way to iterate and discover mounted file systems.

   The mnt_id_req structure
       req.size is used by the kernel to determine which struct mnt_id_req is being passed in, it should  always
       be set to sizeof(struct mnt_id_req).

       req.mnt_id  is  the  parent  mnt_id that we will list from, which can either be LSMT_ROOT which means the
       root mount of  the  current  mount  namespace,  or  a  mount  ID  obtained  from  either  statx(2)  using
       STATX_MNT_ID_UNIQUE or from listmount(2).

       req.param  is  used  to tell the kernel what mount ID to start the list from.  This is useful if multiple
       calls to listmount(2) are required.  This can be set to the last mount ID returned  in  order  to  resume
       from a previous spot in the list.

RETURN VALUE

       On  success,  the  number of entries filled into mnt_ids is returned; 0 if there are no more mounts left.
       On error, -1 is returned, and errno is set to indicate the error.

ERRORS

       EPERM  The caller does not have CAP_SYS_ADMIN in the user namespace.

       EFAULT req or mnt_ids points to a location outside the process's accessible address space.

       EINVAL Invalid flag specified in flags.

       EINVAL req is of insufficient size to be utilized.

       E2BIG  req is too large, the limit is the architectures page size.

       ENOENT The specified req.mnt_id doesn't exist.

       ENOMEM Out of memory (i.e., kernel memory).

STANDARDS

       Linux.

SEE ALSO

       statmount(2), statx(2)

Linux man-pages 6.16                               2025-09-06                                       listmount(2)