How to increase FD_SETSIZE value

[SnipahWUF]

good day! i have a problem regarding the select( ) function... i opened more than 1024 sockets and used FD_SET( ) macro before using select( ) but it seems that when the maximum file descriptor opened reaches more than 1024 it resets to -1. i think this has something to do with the FD_SETSIZE pre-defined constant in /usr/sys/select.h... can someone help me out how to increase its value? thanks in advance...

 

[cfsalmeida]

Max "File descriptors" is limited to 1024 in kernel by default, if you want you can change this by do the following:

i.e. modified /etc/system file and added the following lines:

set rlim_fd_cur=4000
set rlim_fd_max=4000

... reboot, in this case new max descriptors value will be
4000.

Hope this helps,

Carlos Almeida,

 

[SnipahWUF]

FD_SETSIZE value has nothing to do with the maximum open file descriptors... FD_SET macro accepts values up to 1024 only... select manipulates file descriptors as bits so we can think that the actual size is only 128 (128 * 8 bits = 1024 bits)... i need to increase this value in order for FD_SET to accept values larger than 1024...

 

[cfsalmeida]

Yes you are right, I don't explain myself right i mean select() use FD_SETSIZE, which is normally at least equal to the maximum number of descriptors supported by the system, as you certainly know increase is size by having the program define FD_SETSIZE before the inclusion of any header which includes, doesn't work because the limitation is in the select library call, not in the poll system call. Select is hard-wired at a max of 1024 file descriptors. sorry am not a programmer ... can you use poll ? the poll(2) function is preferred over select function when the number of file descriptors exceeds FD_SETSIZE.

Regards,

Carlos Almeida