---
name: "libssh2_channel_write_ex"
section: "3"
platform: "linux"
package: "libssh2"
version: "1.11.1-7"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/libssh2_channel_write_ex"
---

# libssh2\_channel\_write\_ex(3)

write data to a channel stream blocking

## NAME

libssh2\_channel\_write\_ex - write data to a channel stream blocking

## SYNOPSIS

```
#include <libssh2.h>
ssize_t
libssh2_channel_write_ex(LIBSSH2_CHANNEL *channel,
                         int stream_id, char *buf,
                         size_t buflen);
```

## DESCRIPTION

Write data to a channel stream. All channel streams have one standard I/O substream (stream\_id == 0), and may have up to 2^32 extended data streams as identified by the selected *stream\_id*. The SSH2 protocol currently defines a stream ID of 1 to be the stderr substream.

*channel* - active channel stream to write to.

*stream\_id* - substream ID number (e.g. 0 or SSH\_EXTENDED\_DATA\_STDERR)

*buf* - pointer to buffer to write

*buflen* - size of the data to write

*[libssh2\_channel\_write(3)](/libssh2_channel_write/3.md)* and *[libssh2\_channel\_write\_stderr(3)](/libssh2_channel_write_stderr/3.md)* are convenience macros for this function.

*[libssh2\_channel\_write\_ex(3)](/libssh2_channel_write_ex/3.md)* will use as much as possible of the buffer and put it into a single SSH protocol packet. This means that to get maximum performance when sending larger files, you should try to always pass in at least 32K of data to this function.

## RETURN VALUE

Actual number of bytes written or negative on failure. LIBSSH2\_ERROR\_EAGAIN when it would otherwise block. While LIBSSH2\_ERROR\_EAGAIN is a negative number, it is not really a failure per se.

## ERRORS

*LIBSSH2\_ERROR\_ALLOC* - An internal memory allocation call failed.

*LIBSSH2\_ERROR\_SOCKET\_SEND* - Unable to send data on socket.

*LIBSSH2\_ERROR\_CHANNEL\_CLOSED* - The channel has been closed.

*LIBSSH2\_ERROR\_CHANNEL\_EOF\_SENT* - The channel has been requested to be

*LIBSSH2\_ERROR\_BAD\_USE* - This can be returned if you ignored a previous return for LIBSSH2\_ERROR\_EAGAIN and rather than sending the original buffer with the original size, you sent a new buffer with a different size.

closed.

## SEE ALSO

**[libssh2\_channel\_open\_ex(3)](/libssh2_channel_open_ex/3.md)** **[libssh2\_channel\_read\_ex(3)](/libssh2_channel_read_ex/3.md)**