While browsing Linux kernel source code I came across POSIX (Portable Operating System Interface) variable called _POSIX_HOST_NAME_MAX . It defines the maximum length of a host name (not including the terminating null) as returned from the gethostname function.
This variable sets the limit to the number of characters in a hostname under Linux.
$ grep '_POSIX_HOST_NAME_MAX' /usr/include/bits/posix1_lim.h
Output:
#define _POSIX_HOST_NAME_MAX 255
You can change limit and recompile the kernel to get bigger hostname.
See comment below for correct information.
Updated for accuracy.
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{ 3 comments… read them below or add one }
This is a VERY bad idea. The length of hostnames is a standard defined by the RFC’s.
If anyone adjusts this to excess of the standards and has problems, they are just a idiot to be laughed at.
This is one that you are actually wrong on.
The Single Unix Specification version 2 (SuSv2) guarantees ‘Host names are limited to 255 bytes’. POSIX 1003.1-2001 guarantees ‘Host names (not including the terminating NULL) are limited to HOST_NAME_MAX bytes’.
$ grep HOST_NAME_MAX /usr/include/bits/local_lim.h
#define HOST_NAME_MAX 64
$ getconf HOST_NAME_MAX
64
This is part of the c library you use and libc defaults to 64. Changing your kernel and recompiling would still give you a max hostname size of 64 characters including the null termination byte at the end.
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Thanks for correct information, The post has been updated.