---
name: "ldattach"
section: "8"
platform: "linux"
package: "util-linux"
version: "2.42.4-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "openbsd"]
url: "https://new.carta.tech/ldattach"
---

# ldattach(8)

attach a line discipline to a serial line

## NAME

ldattach - attach a line discipline to a serial line

## SYNOPSIS

**ldattach** \[**-1278denoVh**\] \[**-i** *iflag*\] \[**-s** *speed*\] \[**-m** *mtu*\] *ldisc device*

## DESCRIPTION

The **ldattach** daemon opens the specified *device* file (which should refer to a serial device) and attaches the line discipline *ldisc* to it for processing of the sent and/or received data. It then goes into the background keeping the device open so that the line discipline stays loaded.

The line discipline *ldisc* may be specified either by name or by number.

In order to detach the line discipline, [**kill**(1)](/kill/1.md) the **ldattach** process.

With no arguments, **ldattach** prints usage information.

## LINE DISCIPLINES

Depending on the kernel release, the following line disciplines are supported:

**TTY**(**0**)

The default line discipline, providing transparent operation (raw mode) as well as the habitual terminal line editing capabilities (cooked mode).

**SLIP**(**1**)

Serial Line IP (SLIP) protocol processor for transmitting TCP/IP packets over serial lines.

**MOUSE**(**2**)

Device driver for RS232 connected pointing devices (serial mice).

**PPP**(**3**)

Point to Point Protocol (PPP) processor for transmitting network packets over serial lines.

**STRIP**(**4**); **AX25**(**5**); **X25**(**6**)

Line driver for transmitting X.25 packets over asynchronous serial lines.

**6PACK**(**7**); **R3964**(**9**)

Driver for Simatic R3964 module.

**IRDA**(**11**)

Linux IrDa (infrared data transmission) driver - see  \<http://irda.sourceforge.net/\>

**HDLC**(**13**)

Synchronous HDLC driver.

**SYNC\_PPP**(**14**)

Synchronous PPP driver.

**HCI**(**15**)

Bluetooth HCI UART driver.

**GIGASET\_M101**(**16**)

Driver for Siemens Gigaset M101 serial DECT adapter.

**PPS**(**18**)

Driver for serial line Pulse Per Second (PPS) source.

**GSM0710**(**21**)

Driver for GSM 07.10 multiplexing protocol modem (CMUX).

## OPTIONS

- **-1**, **--onestopbit**

  Set the number of stop bits of the serial line to one.

- **-2**, **--twostopbits**

  Set the number of stop bits of the serial line to two.

- **-7**, **--sevenbits**

  Set the character size of the serial line to 7 bits.

- **-8**, **--eightbits**

  Set the character size of the serial line to 8 bits.

- **-d**, **--debug**

  Keep **ldattach** in the foreground so that it can be interrupted or debugged, and to print verbose messages about its progress to standard error output.

- **-e**, **--evenparity**

  Set the parity of the serial line to even.

- **-i**, **--iflag** *value*...

  Set the specified bits in the c\_iflag word of the serial line. The given *value* may be a number or a symbolic name. If *value* is prefixed by a minus sign, the specified bits are cleared instead. Several comma-separated values may be given in order to set and clear multiple bits.

- **-n**, **--noparity**

  Set the parity of the serial line to none.

- **-o**, **--oddparity**

  Set the parity of the serial line to odd.

- **-s**, **--speed** *value*

  Set the speed (the baud rate) of the serial line to the specified *value*.

- **-c**, **--intro-command** *string*

  Define an intro command that is sent through the serial line before the invocation of **ldattach**. E.g. in conjunction with line discipline GSM0710, the command 'AT+CMUX=0\\r' is commonly suitable to switch the modem into the CMUX mode.

- **-p**, **--pause** *value*

  Sleep for *value* seconds before the invocation of **ldattach**. Default is one second.

- **-m**, **--mtu** *value*

  Set maximum frame size for GSM0710 CMUX. If not specified, traditionally the default of 127 have been set by **ldattach**. This differs from 3GPP TS 27.010 default value of 31 bytes, so it is recommended to specify

- **-h**, **--help**

  Display help text and exit.

- **-V**, **--version**

  Display version and exit.

## AUTHORS

*Tilman Schmidt* \<tilman@imap.cc\>

## SEE ALSO

[**inputattach**(1)](/inputattach/1.md), [**ttys**(4)](/ttys/4.md)

## REPORTING BUGS

For bug reports, use the *issue tracker* \<https://github.com/util-linux/util-linux/issues\>.

## AVAILABILITY

The **ldattach** command is part of the util-linux package which can be downloaded from *Linux Kernel Archive* \<https://www.kernel.org/pub/linux/utils/util-linux/\>.