nbd\_connect\_tcp(3) LIBNBD nbd\_connect\_tcp(3)

# [NAME](#NAME)

nbd\_connect\_tcp - connect to NBD server over a TCP port

# [SYNOPSIS](#SYNOPSIS)

```
 #include <libnbd.h>
 int nbd_connect_tcp (
       struct nbd_handle *h, const char *hostname,
       const char *port
     );
```

# [DESCRIPTION](#DESCRIPTION)

Connect (synchronously) to the NBD server listening on "hostname:port". The "port" may be a port name such as "nbd", or it may be a port number as a string such as "10809".

This call returns when the connection has been made. By default, this proceeds all the way to transmission phase, but [**nbd\_set\_opt\_mode**(3)](/man/os/libnbd/nbd_set_opt_mode.3) can be used for manual control over option negotiation performed before transmission phase.

# [RETURN VALUE](#RETURN_VALUE)

If the call is successful the function returns 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", "hostname", "port". For more information see "Non-NULL parameters" in [**libnbd**(3)](/man/os/libnbd/libnbd.3).

# [HANDLE STATE](#HANDLE_STATE)

nbd\_connect\_tcp can be called when the handle is in the following state:

```
 ┌─────────────────────────────────────┬─────────────────────────┐
 │ Handle created, before connecting   │ ✅ allowed              │
 │ Connecting                          │ ❌ error                │
 │ Connecting & handshaking (opt_mode) │ ❌ error                │
 │ Connected to the server             │ ❌ error                │
 │ Connection shut down                │ ❌ error                │
 │ 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_CONNECT_TCP 1
```

# [SEE ALSO](#SEE_ALSO)

[**nbd\_aio\_connect\_tcp**(3)](/man/os/libnbd/nbd_aio_connect_tcp.3), [**nbd\_create**(3)](/man/os/libnbd/nbd_create.3), [**nbd\_set\_opt\_mode**(3)](/man/os/libnbd/nbd_set_opt_mode.3), [**libnbd**(3)](/man/os/libnbd/libnbd.3).

# [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_connect_tcp(3) from libnbd 1.25.7-r2 (Chainguard OS)