The
trace command masquerades under several different names, depending on the operating system that you are using. On Linux it will be
strace, on Solaris you'll use
truss, and SGI will have
padc and
par. All have essentially the same function, which is to display each operating system function call as it is executed. This allows you to follow the execution of a program, such as the Samba server, and will often pinpoint the exact call that is causing the difficulty.
One problem that
trace can highlight is the location of an incorrect version of a dynamically linked library. This can happen if you've downloaded prebuilt binaries of Samba. You'll typically see the offending call at the end of the
trace, just before the program terminates.
A sample
strace output for the Linux operating system follows. This is a small section of a larger file created during the opening of a directory on the Samba server. Each line is a system-call name, and includes its parameters and the return value. If there was an error, the error value (e.g.,
ENOENT) and its explanation are also shown. You can look up the parameter types and the errors that can occur in the appropriate
trace manual page for the operating system that you are using.
chdir("/pcdisk/public") = 0
stat("mini/desktop.ini", 0xbffff7ec) = -1 ENOENT (No such file or directory)
stat("mini", {st_mode=S_IFDIR|0755, st_size=1024, ...}) = 0
stat("mini/desktop.ini", 0xbffff7ec) = -1 ENOENT (No such file or directory)
open("mini", O_RDONLY) = 5
fcntl(5, F_SETFD, FD_CLOEXEC) = 0
fstat(5, {st_mode=S_IFDIR|0755, st_size=1024, ...}) = 0
lseek(5, 0, SEEK_CUR) = 0
SYS_141(0x5, 0xbfffdbbc, 0xedc, 0xbfffdbbc, 0x80ba708) = 196
lseek(5, 0, SEEK_CUR) = 1024
SYS_141(0x5, 0xbfffdbbc, 0xedc, 0xbfffdbbc, 0x80ba708) = 0
close(5) = 0
stat("mini/desktop.ini", 0xbffff86c) = -1 ENOENT (No such file or directory)
write(3, "\0\0\0#\377SMB\10\1\0\2\0\200\1\0"..., 39) = 39
SYS_142(0xff, 0xbffffc3c, 0, 0, 0xbffffc08) = 1
read(3, "\0\0\0?", 4) = 4
read(3, "\377SMBu\0\0\0\0\0\0\0\0\0\0\0\0"..., 63) = 63
time(NULL) = 896143871
This example shows several
stat calls failing to find the files they were expecting. You don't have to be a expert to see that the file
desktop.ini is missing from that directory. In fact, many difficult problems can be identified by looking for obvious, repeatable errors with
trace. Often, you need not look farther than the last message before a crash.
