lp(4) — Linux manual page


LP(4)                     Linux Programmer's Manual                    LP(4)

NAME         top

       lp - line printer devices

SYNOPSIS         top

       #include <linux/lp.h>


       lp[0–2] are character devices for the parallel line printers; they
       have major number 6 and minor number 0–2.  The minor numbers
       correspond to the printer port base addresses 0x03bc, 0x0378, and
       0x0278.  Usually they have mode 220 and are owned by user root and
       group lp.  You can use printer ports either with polling or with
       interrupts.  Interrupts are recommended when high traffic is
       expected, for example, for laser printers.  For typical dot matrix
       printers, polling will usually be enough.  The default is polling.

DESCRIPTION         top

       The following ioctl(2) calls are supported:

       int ioctl(int fd, LPTIME, int arg)
              Sets the amount of time that the driver sleeps before
              rechecking the printer when the printer's buffer appears to be
              filled to arg.  If you have a fast printer, decrease this
              number; if you have a slow printer, then increase it.  This is
              in hundredths of a second, the default 2 being 0.02 seconds.
              It influences only the polling driver.

       int ioctl(int fd, LPCHAR, int arg)
              Sets the maximum number of busy-wait iterations which the
              polling driver does while waiting for the printer to get ready
              for receiving a character to arg.  If printing is too slow,
              increase this number; if the system gets too slow, decrease
              this number.  The default is 1000.  It influences only the
              polling driver.

       int ioctl(int fd, LPABORT, int arg)
              If arg is 0, the printer driver will retry on errors,
              otherwise it will abort.  The default is 0.

       int ioctl(int fd, LPABORTOPEN, int arg)
              If arg is 0, open(2) will be aborted on error, otherwise error
              will be ignored.  The default is to ignore it.

       int ioctl(int fd, LPCAREFUL, int arg)
              If arg is 0, then the out-of-paper, offline, and error signals
              are required to be false on all writes, otherwise they are
              ignored.  The default is to ignore them.

       int ioctl(int fd, LPWAIT, int arg)
              Sets the number of busy waiting iterations to wait before
              strobing the printer to accept a just-written character, and
              the number of iterations to wait before turning the strobe off
              again, to arg.  The specification says this time should be 0.5
              microseconds, but experience has shown the delay caused by the
              code is already enough.  For that reason, the default value is
              0.  This is used for both the polling and the interrupt

       int ioctl(int fd, LPSETIRQ, int arg)
              This ioctl(2) requires superuser privileges.  It takes an int
              containing the new IRQ as argument.  As a side effect, the
              printer will be reset.  When arg is 0, the polling driver will
              be used, which is also default.

       int ioctl(int fd, LPGETIRQ, int *arg)
              Stores the currently used IRQ in arg.

       int ioctl(int fd, LPGETSTATUS, int *arg)
              Stores the value of the status port in arg.  The bits have the
              following meaning:

              LP_PBUSY     inverted busy input, active high
              LP_PACK      unchanged acknowledge input, active low
              LP_POUTPA    unchanged out-of-paper input, active high
              LP_PSELECD   unchanged selected input, active high
              LP_PERRORP   unchanged error input, active low

              Refer to your printer manual for the meaning of the signals.
              Note that undocumented bits may also be set, depending on your

       int ioctl(int fd, LPRESET)
              Resets the printer.  No argument is used.

FILES         top


SEE ALSO         top

       chmod(1), chown(1), mknod(1), lpcntl(8), tunelp(8)

COLOPHON         top

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       latest version of this page, can be found at

Linux                            2020-08-13                            LP(4)