FILEMON(4FREEBSD) - man page online | special files

The filemon device.

June 14, 2013
FILEMON(4)                         BSD Kernel Interfaces Manual                        FILEMON(4)


filemon — the filemon device


#include <dev/filemon/filemon.h>


The filemon device allows a process to collect file operations data of its children. The device /dev/filemon responds to two ioctl(2) calls. System calls are denoted using the following single letters: ‘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) for read ‘S’ stat(2) ‘W’ open(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 cap‐ tured.


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.


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.




#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 buf‐ fer contents to it.


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


A filemon device appeared in FreeBSD 9.1.
BSD June 14, 2013 BSD
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filemon(4freebsd) referred by bmake(1)
refer to chdir(2) | dtrace(1) | _exit(2) | fork(2) | ioctl(2) | link(2) | open(2) | rename(2) | stat(2) | symlink(2) | unlink(2) | vfork(2)