nbd\_get\_size(3) LIBNBD nbd\_get\_size(3)

# [NAME](#NAME)

nbd\_get\_size - return the export size

# [SYNOPSIS](#SYNOPSIS)

```
 #include <libnbd.h>
 int64_t nbd_get_size (
           struct nbd_handle *h
         );
```

# [DESCRIPTION](#DESCRIPTION)

Returns the size in bytes of the NBD export.

Note that this call fails with "EOVERFLOW" for an unlikely server that advertises a size which cannot fit in a 64-bit signed integer.

[**nbdinfo**(1)](/man/os/libnbd/nbdinfo.1) *--size* option is a way to access this API from shell scripts.

This call does not block, because it returns data that is saved in the handle from the NBD protocol handshake.

# [RETURN VALUE](#RETURN_VALUE)

This call returns a 64 bit signed integer ≥ 0.

# [ERRORS](#ERRORS)

On error -1 is returned.

Refer to "ERROR HANDLING" in [**libnbd**(3)](/man/os/libnbd/libnbd.3) for how to get further details of the error.

The following parameters must not be NULL: "h". For more information see "Non-NULL parameters" in [**libnbd**(3)](/man/os/libnbd/libnbd.3).

# [HANDLE STATE](#HANDLE_STATE)

nbd\_get\_size can be called when the handle is in the following states:

```
 ┌─────────────────────────────────────┬─────────────────────────┐
 │ Handle created, before connecting   │ ❌ error                │
 │ Connecting                          │ ❌ error                │
 │ Connecting & handshaking (opt_mode) │ ✅ allowed              │
 │ Connected to the server             │ ✅ allowed              │
 │ Connection shut down                │ ✅ allowed              │
 │ Handle dead                         │ ❌ error                │
 └─────────────────────────────────────┴─────────────────────────┘
```

# [VERSION](#VERSION)

This function first appeared in libnbd 1.0.

If you need to test if this function is available at compile time check if the following macro is defined:

```
 #define LIBNBD_HAVE_NBD_GET_SIZE 1
```

# [EXAMPLE](#EXAMPLE)

This example is also available as *examples/get-size.c* in the libnbd source code.

```
 /* This example shows how to connect to an NBD
  * server and read the size of the disk.
  *
  * You can test it with nbdkit like this:
  *
  * nbdkit -U - memory 1M \
  *   --run './get-size $unixsocket'
  */
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdint.h>
 #include <inttypes.h>
 #include <libnbd.h>
 int
 main (int argc, char *argv[])
 {
   struct nbd_handle *nbd;
   int64_t size;
   if (argc != 2) {
     fprintf (stderr, "%s socket\n", argv[0]);
     exit (EXIT_FAILURE);
   }
   /* Create the libnbd handle. */
   nbd = nbd_create ();
   if (nbd == NULL) {
     fprintf (stderr, "%s\n", nbd_get_error ());
     exit (EXIT_FAILURE);
   }
   /* Connect to the NBD server over a
    * Unix domain socket.
    */
   if (nbd_connect_unix (nbd, argv[1]) == -1) {
     fprintf (stderr, "%s\n", nbd_get_error ());
     exit (EXIT_FAILURE);
   }
   /* Read the size in bytes and print it. */
   size = nbd_get_size (nbd);
   if (size == -1) {
     fprintf (stderr, "%s\n", nbd_get_error ());
     exit (EXIT_FAILURE);
   }
   printf ("%s: size = %" PRIi64 " bytes\n",
           argv[1], size);
   /* Close the libnbd handle. */
   nbd_close (nbd);
   exit (EXIT_SUCCESS);
 }
```

# [SEE ALSO](#SEE_ALSO)

[**nbd\_create**(3)](/man/os/libnbd/nbd_create.3), [**nbd\_opt\_info**(3)](/man/os/libnbd/nbd_opt_info.3), "Size of the export" in [**libnbd**(3)](/man/os/libnbd/libnbd.3), [**libnbd**(3)](/man/os/libnbd/libnbd.3), [**nbdinfo**(1)](/man/os/libnbd/nbdinfo.1).

# [AUTHORS](#AUTHORS)

Eric Blake

Richard W.M. Jones

# [COPYRIGHT](#COPYRIGHT)

Copyright Red Hat

# [LICENSE](#LICENSE)

This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

2026-09-11 libnbd-1.25.7

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Document: nbd_get_size(3) from libnbd 1.25.7-r2 (Chainguard OS)