strace Use Example - The Networked Client (Cont.) The, libraries used for host names lookup are loaded: open("/opt/xmps/lib/libnss_files.so.2", O_RDONLY) = -1 ENOENT (No such file or directory) open("/etc/ld.so.cache", O_RDONLY) = 3 fstat64(3, {st_mode=S_IFREG|0644, st_size=58807, ...}) = 0 old_mmap(NULL, 58807, PROT_READ, MAP_PRIVATE, 3, 0) = 0x40013000 close(3) = 0 open("/lib/libnss_files.so.2", O_RDONLY) = 3 read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\320\34"..., 1024) = 1024 fstat64(3, {st_mode=S_IFREG|0755, st_size=42897, ...}) = 0 old_mmap(NULL, 39460, PROT_READ|PROT_EXEC, MAP_PRIVATE, 3, 0) = 0x401ae000 mprotect(0x401b7000, 2596, PROT_NONE) = 0 old_mmap(0x401b7000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED, 3, 0x8000) = 0x401b7000 close(3) = 0 munmap(0x40013000, 58807) = 0 then the application looks up data in /etc/services. 'man services' for more info: open("/etc/services", O_RDONLY) = 3 fcntl64(3, F_GETFD) = 0 fcntl64(3, F_SETFD, FD_CLOEXEC) = 0 fstat64(3, {st_mode=S_IFREG|0644, st_size=19891, ...}) = 0 old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x40013000 read(3, "# /etc/services:\n# $Id: services"..., 4096) = 4096 close(3) = 0 munmap(0x40013000, 4096) = 0