---
name: "nbd_trim"
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_trim"
---

# nbd\_trim(3)

send trim command to the NBD server

## NAME

nbd\_trim - send trim command to the NBD server

## SYNOPSIS

```
 #include <libnbd.h>
 int nbd_trim (
       struct nbd_handle *h, uint64_t count,
       uint64_t offset, uint32_t flags
     );
```

## DESCRIPTION

Issue a trim command to the NBD server, which if supported by the server causes a hole to be punched in the backing store starting at `"offset"` and ending at `"offset"` + `"count"` - 1. The call returns when the command has been acknowledged by the server, or there is an error.  Note this will generally return an error if [**nbd\_can\_trim**(3)](/nbd_can_trim/3.md) is false or [**nbd\_is\_read\_only**(3)](/nbd_is_read_only/3.md) is true.

Note that not all servers can support a `"count"` of 4GiB or larger; [**nbd\_get\_extended\_headers\_negotiated**(3)](/nbd_get_extended_headers_negotiated/3.md) indicates which servers will parse a request larger than 32 bits. The NBD protocol does not yet have a way for a client to learn if the server will enforce an even smaller maximum trim size, although a future extension may add a constraint visible in [**nbd\_get\_block\_size**(3)](/nbd_get_block_size/3.md).

The `"flags"` parameter may be `0` for no flags, or may contain `"LIBNBD_CMD_FLAG_FUA"` meaning that the server should not return until the data has been committed to permanent storage (if that is supported - some servers cannot do this, see [**nbd\_can\_fua**(3)](/nbd_can_fua/3.md)).

By default, libnbd will reject attempts to use this function with parameters that are likely to result in server failure, such as requesting an unknown command flag.  The [**nbd\_set\_strict\_mode**(3)](/nbd_set_strict_mode/3.md) function can be used to alter which scenarios should await a server reply rather than failing fast.

## RETURN VALUE

If the call is successful the function returns `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\_trim can be called when the handle is in the following state:

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

## SEE ALSO

[**nbd\_aio\_trim**(3)](/nbd_aio_trim/3.md), [**nbd\_can\_fua**(3)](/nbd_can_fua/3.md), [**nbd\_can\_trim**(3)](/nbd_can_trim/3.md), [**nbd\_create**(3)](/nbd_create/3.md), [**nbd\_get\_block\_size**(3)](/nbd_get_block_size/3.md), [**nbd\_get\_extended\_headers\_negotiated**(3)](/nbd_get_extended_headers_negotiated/3.md), [**nbd\_is\_read\_only**(3)](/nbd_is_read_only/3.md), [**nbd\_set\_strict\_mode**(3)](/nbd_set_strict_mode/3.md), [**libnbd**(3)](/libnbd/3.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