---
title: IOLogv
framework: kernel
role: symbol
role_heading: Function
path: kernel/1575323-iologv
---

# IOLogv

Log a message to console in text mode, and /var/log/system.log.

## Declaration

```occ
int IOLogv(const char *format, va_list ap);
```

```occ
void IOLogv(const char *format, va_list ap);
```

## Parameters

- `format`: A printf() style format string (see printf(3) documentation).
- `ap`: stdarg(3) style variable arguments.

## Discussion

Discussion This function allows a driver to log diagnostic information to the screen during verbose boots, and to a log file found at /var/log/system.log. IOLogv should not be called from interrupt context.

## See Also

### Logging

- [OS_os_log](kernel/os_os_log.md)
- [IOLog](kernel/1575337-iolog.md)
- [os_log_create](kernel/1643798-os_log_create.md)
- [os_log_debug_enabled](kernel/1643808-os_log_debug_enabled.md)
- [os_log_info_enabled](kernel/1643817-os_log_info_enabled.md)