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ldattach - Man Page

attach a line discipline to a serial line


ldattach [-1278denoVh] [-i iflag] [-s speed] ldisc device


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) the ldattach process.

With no arguments, ldattach prints usage information.

Line Disciplines

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


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


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


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


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.


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


Synchronous HDLC driver.


Synchronous PPP driver.


Bluetooth HCI UART driver.


Driver for Siemens Gigaset M101 serial DECT adapter.


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


Driver for GSM 07.10 multiplexing protocol modem (CMUX).


-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.

-h,  --help

Display help text and exit.

-V,  --version

Print version and exit.


Tilman Schmidt

See Also

inputattach(1), ttys(4)

Reporting Bugs

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


The ldattach command is part of the util-linux package which can be downloaded from Linux Kernel Archive.

Referenced By

ioctl_tty(2), ntp-refclock(8).

2024-04-24 util-linux 2.40.2 System Administration