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FILEMON(4)		     Kernel Interfaces Manual		      FILEMON(4)

NAME
     filemon -- the filemon device

SYNOPSIS
     device filemon

     #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 using a non-native ABI may not be fully au-
     dited.  It is intended for auditing of processes for the purpose of  deter-
     mining  their  dependencies  using 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'     execve(2)
     `F'     fork(2), vfork(2)
     `L'     link(2), linkat(2), symlink(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 de-
			scriptor.

     [EINVAL]		The file descriptor has an invalid type  and  cannot  be
			used for tracing.

     [EBADF]		The  file  descriptor is invalid or not opened for writ-
			ing.

     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 ar-
			gument, resulting in no log entry for the system call.

     [ENAMETOOLONG]	An  argument  for a traced system call was too long, re-
			sulting 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 <errno.h>
     #include <unistd.h>

     static void
     open_filemon(void)
     {
	     pid_t child, wait_rv;
	     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 if (child == -1)
		     err(1, "Cannot fork child");
	     else {
		     while ((wait_rv = wait(&child)) == -1 &&
			 errno == EINTR)
			     ;
		     if (wait_rv == -1)
			     err(1, "cannot wait for 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.

FreeBSD ports 15.quarterly	 April 19, 2025 		      FILEMON(4)

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