LDATTACH(8) System Administration LDATTACH(8)

# [NAME](#NAME)

ldattach - attach a line discipline to a serial line

# [SYNOPSIS](#SYNOPSIS)

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

# [DESCRIPTION](#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)](/man/os/util-linux/kill.1) the **ldattach** process.

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

# [LINE DISCIPLINES](#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](#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](#AUTHORS)

*Tilman Schmidt* <tilman@imap.cc>

# [SEE ALSO](#SEE_ALSO)

[**inputattach**(1)](/man/os/util-linux/inputattach.1), [**ttys**(4)](/man/os/util-linux/ttys.4)

# [REPORTING BUGS](#REPORTING_BUGS)

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

# [AVAILABILITY](#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/>.

2026-10-30 util-linux 2.42.4

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Document: ldattach(8) from util-linux 2.42.4-r2 (Chainguard OS)