Thanks for persevering with me guys :-) Daniel, changing # X11 X11_DIR = /usr to # X11 X11_DIR = /usr/lib64 Gives the same error message Wayne, The result of ls -l /usr/lib64/libXext* [chxcja@amber c]$ ls -l /usr/lib64/libXext* lrwxrwxrwx 1 root root 16 Jul 10 15:34 /usr/lib64/libXext.so.6 -> libXext.so.6.4.0 -rwxr-xr-x 1 root root 72424 Jan 30 2007 /usr/lib64/libXext.so.6.4.0 So there is definitely libXext present. The result of make clean; make ( I have tried it with both X11_DIR = /usr/lib64 and X11_DIR = /usr/ but it gives the same error) [chxcja@amber c]$ make clean ; make cd memops/global; make clean make[1]: Entering directory `/home/chxcja/ccpnmr/ccpnmr1.0/c/memops/global' rm *.o make[1]: Leaving directory `/home/chxcja/ccpnmr/ccpnmr1.0/c/memops/global' cd ccp/structure; make clean make[1]: Entering directory `/home/chxcja/ccpnmr/ccpnmr1.0/c/ccp/structure' rm *.o rm: cannot remove `*.o': No such file or directory make[1]: *** [clean] Error 1 make[1]: Leaving directory `/home/chxcja/ccpnmr/ccpnmr1.0/c/ccp/structure' make: *** [structure_clean] Error 2 cd memops/global; make make[1]: Entering directory `/home/chxcja/ccpnmr/ccpnmr1.0/c/memops/global' cc -c -O -DDO_NOT_HAVE_MALLOC -fPIC utility.c cc -c -I/home/chxcja/ccpnmr/python2.4/include/python2.4 -O -DDO_NOT_HAVE_MALLOC -fPIC python_util.c cc -c -O -DDO_NOT_HAVE_MALLOC -fPIC hash_list.c cc -c -O -DDO_NOT_HAVE_MALLOC -fPIC hash_table.c hash_table.c: In function ‘hash_pointers’: hash_table.c:86: warning: cast from pointer to integer of different size cc -c -O -DDO_NOT_HAVE_MALLOC -fPIC mem_cache.c cc -c -O -DDO_NOT_HAVE_MALLOC -fPIC mutex.c cc -c -I/home/chxcja/ccpnmr/python2.4/include/python2.4 -O -DDO_NOT_HAVE_MALLOC -fPIC py_mem_cache.c cc -c -O -DDO_NOT_HAVE_MALLOC -fPIC block_file.c cc -c -O -DDO_NOT_HAVE_MALLOC -fPIC int_array.c cc -c -I/home/chxcja/ccpnmr/python2.4/include/python2.4 -O -DDO_NOT_HAVE_MALLOC -fPIC py_block_file.c cc -shared -o BlockFile.so utility.o python_util.o hash_list.o hash_table.o mem_cache.o mutex.o py_mem_cache.o block_file.o int_array.o py_block_file.o cc -c -DNEED_GLUT_INIT -I/home/chxcja/ccpnmr/python2.4/include/python2.4 -I/usr/lib64/include -I/home/chxcja/ccpnmr/tcl8.4/include -I/home/chxcja/ccpnmr/tk8.4/include -I/home/chxcja/ccpnmr/mesa6.0/include -O -DDO_NOT_HAVE_MALLOC -fPIC gl_handler.c cc -c -DUSE_GL_FALSE -I/home/chxcja/ccpnmr/python2.4/include/python2.4 -I/usr/lib64/include -I/home/chxcja/ccpnmr/tcl8.4/include -I/home/chxcja/ccpnmr/tk8.4/include -I/home/chxcja/ccpnmr/mesa6.0/include -O -DDO_NOT_HAVE_MALLOC -fPIC py_gl_handler.c cc -c -I/home/chxcja/ccpnmr/python2.4/include/python2.4 -I/usr/lib64/include -I/home/chxcja/ccpnmr/tcl8.4/include -I/home/chxcja/ccpnmr/tk8.4/include -O -DDO_NOT_HAVE_MALLOC -fPIC py_tk_util.c cc -c -O -DDO_NOT_HAVE_MALLOC -fPIC w32func.c cc -shared -o GlHandler.so -L/usr/lib64/lib64 -L/home/chxcja/ccpnmr/tcl8.4/lib -L/home/chxcja/ccpnmr/tk8.4/lib -L/home/chxcja/ccpnmr/mesa6.0/lib \ utility.o python_util.o gl_handler.o py_gl_handler.o py_tk_util.o w32func.o -lglut -lGLU -lGL -ltk8.4 -ltcl8.4 -lX11 -lXext -lm /usr/bin/ld: cannot find -lXext collect2: ld returned 1 exit status make[1]: *** [GlHandler.so] Error 1 make[1]: Leaving directory `/home/chxcja/ccpnmr/ccpnmr1.0/c/memops/global' make: *** [global] Error 2