NAME

       filemon — the filemon device

SYNOPSIS

       #include <dev/filemon/filemon.h>

DESCRIPTION

       The  filemon  device  allows  a  process  to  collect  file  operations data of its children.  The device
       /dev/filemon responds to two ioctl(2) calls.

       filemon is not intended to be a security auditing tool.  Many system calls are not tracked  and  binaries
       of  foreign  ABI  will not be fully audited.  It is intended for auditing of processes for the purpose of
       determining its dependencies in an efficient and easily parsable format.  An example of this  is  make(1)
       which uses this module with .MAKE.MODE=meta to handle incremental builds more smartly.

       System calls are denoted using the following single letters:

       ‘A’     openat(2).  The next log entry may be lacking an absolute path or be inaccurate.
       ‘C’     chdir(2)
       ‘D’     unlink(2)
       ‘E’     exec(2)
       ‘F’     fork(2), vfork(2)
       ‘L’     link(2), linkat(2), symlink(2), symlinkat(2)
       ‘M’     rename(2)
       ‘R’     open(2) or openat(2) for read
       ‘W’     open(2) or openat(2) for write
       ‘X’     _exit(2)

       Note  that  ‘R’  following  ‘W’  records  can represent a single open(2) for R/W, or two separate open(2)
       calls, one for ‘R’ and one for ‘W’.  Note that only successful system calls are captured.

IOCTLS

       User mode programs communicate with the filemon driver through a number of  ioctls  which  are  described
       below.  Each takes a single argument.

       FILEMON_SET_FD   Write the internal tracing buffer to the supplied open file descriptor.

       FILEMON_SET_PID  Child  process  ID to trace.  This should normally be done under the control of a parent
                        in the child after fork(2) but before anything else.  See the example below.

RETURN VALUES

       The ioctl() function returns the value 0 if successful; otherwise the value -1 is returned and the global
       variable errno is set to indicate the error.

ERRORS

       The ioctl() system call with FILEMON_SET_FD will fail if:

       [EEXIST]           The filemon handle is already associated with a file descriptor.

       The ioctl() system call with FILEMON_SET_PID will fail if:

       [ESRCH]            No process having the specified process ID exists.

       [EBUSY]            The process ID specified is already being traced and was not the current process.

       The close() system call on the filemon file descriptor may fail with the  errors  from  write(2)  if  any
       error is encountered while writing the log.  It may also fail if:

       [EFAULT]           An  invalid  address  was  used for a traced system call argument, resulting in no log
                          entry for the system call.

       [ENAMETOOLONG]     An argument for a traced system call was too long, resulting in no log entry  for  the
                          system call.

FILES

       /dev/filemon

EXAMPLES

       #include <sys/types.h>
       #include <sys/stat.h>
       #include <sys/wait.h>
       #include <sys/ioctl.h>
       #include <dev/filemon/filemon.h>
       #include <fcntl.h>
       #include <err.h>
       #include <unistd.h>

       static void
       open_filemon(void)
       {
               pid_t child;
               int fm_fd, fm_log;

               if ((fm_fd = open("/dev/filemon", O_RDWR | O_CLOEXEC)) == -1)
                       err(1, "open(\"/dev/filemon\", O_RDWR)");
               if ((fm_log = open("filemon.out",
                   O_CREAT | O_WRONLY | O_TRUNC | O_CLOEXEC, DEFFILEMODE)) == -1)
                       err(1, "open(filemon.out)");

               if (ioctl(fm_fd, FILEMON_SET_FD, &fm_log) == -1)
                       err(1, "Cannot set filemon log file descriptor");

               if ((child = fork()) == 0) {
                       child = getpid();
                       if (ioctl(fm_fd, FILEMON_SET_PID, &child) == -1)
                               err(1, "Cannot set filemon PID");
                       /* Do something here. */
               } else {
                       wait(&child);
                       close(fm_fd);
               }
       }

       Creates  a  file named filemon.out and configures the filemon device to write the filemon buffer contents
       to it.

SEE ALSO

       dtrace(1), ktrace(1), script(1), truss(1), ioctl(2)

HISTORY

       A filemon device appeared in FreeBSD 9.1.

BUGS

       Unloading the module may panic the system, thus requires using kldunload -f.

Debian                                           March 22, 2016                                       FILEMON(4)