---
name: "nbd_get_size"
section: "3"
platform: "linux"
package: "libnbd"
version: "1.24.4-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/nbd_get_size"
---

# nbd\_get\_size(3)

return the export size

## NAME

nbd\_get\_size - return the export size

## SYNOPSIS

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

## 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)](/nbdinfo/1.md) *--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

This call returns a 64 bit signed integer ≥ `0`.

## ERRORS

On error `-1` is returned.

Refer to "ERROR HANDLING" in [**libnbd**(3)](/libnbd/3.md) 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)](/libnbd/3.md).

## 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

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

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

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

## AUTHORS

Eric Blake

Richard W.M. Jones

## COPYRIGHT

Copyright Red Hat

## 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