I am running ruby1.9 on Debian 5, and did not manage to install 'unicorn' with rubygems. I got this error and do not really know how to solve it.

Do you have any idea of the possible root cause ?

> gem install unicorn


Building native extensions.  This could take a while...
ERROR:  Error installing unicorn:
ERROR: Failed to build gem native extension.

    /usr/bin/ruby1.9 extconf.rb
checking for CLOCK_MONOTONIC in time.h... yes
checking for clockid_t in time.h... yes
checking for clock_gettime() in -lrt... yes
checking for t_open() in -lnsl... no
checking for socket() in -lsocket... no
checking for poll() in poll.h... yes
checking for getaddrinfo() in sys/types.h,sys/socket.h,netdb.h... yes
checking for getnameinfo() in sys/types.h,sys/socket.h,netdb.h... yes
checking for struct sockaddr_storage in sys/types.h,sys/socket.h... yes
checking for accept4() in sys/socket.h... no
checking for sys/select.h... yes
checking for ruby/io.h... yes
checking for rb_io_t.fd in ruby.h,ruby/io.h... yes
checking for rb_io_t.mode in ruby.h,ruby/io.h... yes
checking for rb_io_t.pathv in ruby.h,ruby/io.h... no
checking for struct RFile in ruby.h,ruby/io.h... yes
checking size of struct RFile in ruby.h,ruby/io.h... 24
checking for struct RObject... no
checking size of int... 4
checking for rb_io_ascii8bit_binmode()... no
checking for rb_thread_blocking_region()... yes
checking for rb_thread_io_blocking_region()... no
checking for rb_str_set_len()... yes
checking for rb_time_interval()... yes
checking for rb_wait_for_single_fd()... no
creating Makefile

make cc -I. -I/usr/include/ruby-1.9.0/x86_64-linux -I/usr/include/ruby-1.9.0 -I. -DHAVE_TYPE_CLOCKID_T -DHAVE_POLL -DHAVE_GETADDRINFO -DHAVE_GETNAMEINFO -DHAVE_TYPE_STRUCT_SOCKADDR_STORAGE -DHAVE_SYS_SELECT_H -DHAVE_RUBY_IO_H -DHAVE_RB_IO_T_FD -DHAVE_ST_FD -DHAVE_RB_IO_T_MODE -DHAVE_ST_MODE -DHAVE_TYPE_STRUCT_RFILE -DSIZEOF_STRUCT_RFILE=24 -DSIZEOF_INT=4 -DHAVE_RB_THREAD_BLOCKING_REGION -DHAVE_RB_STR_SET_LEN -DHAVE_RB_TIME_INTERVAL -D_GNU_SOURCE -DPOSIX_C_SOURCE=1-D_POSIX_C_SOURCE=200112L -fPIC -fno-strict-aliasing -g -g -O2 -O2 -g -Wall -Wno-parentheses -fPIC -o kgio_ext.o -c kgio_ext.c cc -I. -I/usr/include/ruby-1.9.0/x86_64-linux -I/usr/include/ruby-1.9.0 -I. -DHAVE_TYPE_CLOCKID_T -DHAVE_POLL -DHAVE_GETADDRINFO -DHAVE_GETNAMEINFO -DHAVE_TYPE_STRUCT_SOCKADDR_STORAGE -DHAVE_SYS_SELECT_H -DHAVE_RUBY_IO_H -DHAVE_RB_IO_T_FD -DHAVE_ST_FD -DHAVE_RB_IO_T_MODE -DHAVE_ST_MODE -DHAVE_TYPE_STRUCT_RFILE -DSIZEOF_STRUCT_RFILE=24 -DSIZEOF_INT=4 -DHAVE_RB_THREAD_BLOCKING_REGION -DHAVE_RB_STR_SET_LEN -DHAVE_RB_TIME_INTERVAL -D_GNU_SOURCE -DPOSIX_C_SOURCE=1-D_POSIX_C_SOURCE=200112L -fPIC -fno-strict-aliasing -g -g -O2 -O2 -g -Wall -Wno-parentheses -fPIC -o autopush.o -c autopush.c cc -I. -I/usr/include/ruby-1.9.0/x86_64-linux -I/usr/include/ruby-1.9.0 -I. -DHAVE_TYPE_CLOCKID_T -DHAVE_POLL -DHAVE_GETADDRINFO -DHAVE_GETNAMEINFO -DHAVE_TYPE_STRUCT_SOCKADDR_STORAGE -DHAVE_SYS_SELECT_H -DHAVE_RUBY_IO_H -DHAVE_RB_IO_T_FD -DHAVE_ST_FD -DHAVE_RB_IO_T_MODE -DHAVE_ST_MODE -DHAVE_TYPE_STRUCT_RFILE -DSIZEOF_STRUCT_RFILE=24 -DSIZEOF_INT=4 -DHAVE_RB_THREAD_BLOCKING_REGION -DHAVE_RB_STR_SET_LEN -DHAVE_RB_TIME_INTERVAL -D_GNU_SOURCE -DPOSIX_C_SOURCE=1-D_POSIX_C_SOURCE=200112L -fPIC -fno-strict-aliasing -g -g -O2 -O2 -g -Wall -Wno-parentheses -fPIC -o wait.o -c wait.c cc -I. -I/usr/include/ruby-1.9.0/x86_64-linux -I/usr/include/ruby-1.9.0 -I. -DHAVE_TYPE_CLOCKID_T -DHAVE_POLL -DHAVE_GETADDRINFO -DHAVE_GETNAMEINFO -DHAVE_TYPE_STRUCT_SOCKADDR_STORAGE -DHAVE_SYS_SELECT_H -DHAVE_RUBY_IO_H -DHAVE_RB_IO_T_FD -DHAVE_ST_FD -DHAVE_RB_IO_T_MODE -DHAVE_ST_MODE -DHAVE_TYPE_STRUCT_RFILE -DSIZEOF_STRUCT_RFILE=24 -DSIZEOF_INT=4 -DHAVE_RB_THREAD_BLOCKING_REGION -DHAVE_RB_STR_SET_LEN -DHAVE_RB_TIME_INTERVAL -D_GNU_SOURCE -DPOSIX_C_SOURCE=1-D_POSIX_C_SOURCE=200112L -fPIC -fno-strict-aliasing -g -g -O2 -O2 -g -Wall -Wno-parentheses -fPIC -o connect.o -c connect.c cc -I. -I/usr/include/ruby-1.9.0/x86_64-linux -I/usr/include/ruby-1.9.0 -I. -DHAVE_TYPE_CLOCKID_T -DHAVE_POLL -DHAVE_GETADDRINFO -DHAVE_GETNAMEINFO -DHAVE_TYPE_STRUCT_SOCKADDR_STORAGE -DHAVE_SYS_SELECT_H -DHAVE_RUBY_IO_H -DHAVE_RB_IO_T_FD -DHAVE_ST_FD -DHAVE_RB_IO_T_MODE -DHAVE_ST_MODE -DHAVE_TYPE_STRUCT_RFILE -DSIZEOF_STRUCT_RFILE=24 -DSIZEOF_INT=4 -DHAVE_RB_THREAD_BLOCKING_REGION -DHAVE_RB_STR_SET_LEN -DHAVE_RB_TIME_INTERVAL -D_GNU_SOURCE -DPOSIX_C_SOURCE=1-D_POSIX_C_SOURCE=200112L -fPIC -fno-strict-aliasing -g -g -O2 -O2 -g -Wall -Wno-parentheses -fPIC -o poll.o -c poll.c

poll.c:11:18: error: st.h: No such file or directory
poll.c: In function 'do_poll':
poll.c:148: error: 'RUBY_UBF_IO' undeclared (first use in this function)
poll.c:148: error: (Each undeclared identifier is reported only once
poll.c:148: error: for each function it appears in.)
make: *** [poll.o] Error 1


Gem files will remain installed in /usr/lib/ruby/gems/1.9.0/gems/kgio-2.5.0 for inspection.
Results logged to /usr/lib/ruby/gems/1.9.0/gems/kgio-2.5.0/ext/kgio/gem_make.out