> On Wed, 2005-03-02 at 17:47 +0530, Reddy V, Ravinder (Ravinder) wrote: >> Hi, >> >> Can anyone please let me know the system variable which holds the pseudo >> terminal limit in fedora linux. >> Also please let me know the filename where this variable is present, and how >> to change this variable value? > > If you look in Documentation/devices.txt in the kernel sources, you will > see that device major numbers 136-143 reserved for Unix98 pseudo-TTY > devices. That makes 8 x 256 total available under the current device > allocation scheme. > > However, if you look in include/linux/tty.h you see this: > > #define NR_UNIX98_PTY_DEFAULT 4096 /* Default maximum for Unix98 ptys */ > #define NR_UNIX98_PTY_MAX (1 << MINORBITS) /* Absolute limit */ > > and in include/linux/kdev_t.h > > #define MINORBITS 20 > > Which gives a maximum of 1048576. So then looking in drivers/char/pty.c > > /* Unix98 devices */ > #ifdef CONFIG_UNIX98_PTYS > /* > * sysctl support for setting limits on the number of Unix98 ptys allocated. > * Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly. > */ > int pty_limit = NR_UNIX98_PTY_DEFAULT; > static int pty_limit_min = 0; > static int pty_limit_max = NR_UNIX98_PTY_MAX; > > And from sysctl: > > kernel.pty.max = 4096 > > So you can set it either by echoing a value into: > > /proc/sys/kernel/pty/max > > Or by using > > sysctl -w kernel.pty.max=<value> > > If you want to set it permanently, add a line to /etc/sysctl.conf and it > will get loaded at boot time. > > -- > C. Linus Hicks <lhicks at nc dot rr dot com> The above was posted earlier this month. What I don't understand is how to reconcile the maximum of 8 x 256 (2048) total devices available based on major/minor device numbers with the default of 4096 or the theoretical max of 1048576. Is there something else at work here?
