filemon(4) - NetBSD Manual Pages

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FILEMON(4)              NetBSD Kernel Interfaces Manual             FILEMON(4)


NAME
filemon -- track interesting system calls
SYNOPSIS
pseudo-device filemon
DESCRIPTION
In normal situations, filemon is not built-in to the kernel, and a call to open /dev/filemon will auto-load the filemon module (see module(7) for more details). (Although not recommended, the filemon facility can be included in a ker- nel build by adding pseudo-device filemon to the kernel configuration file.) filemon provides a means for tracking the successful system calls per- formed by a process and its descendants. It is used by make(1) to track the activities of build scripts, for the purpose of automatically learn- ing dependencies. The data captured by filemon for the script n=`wc -l /etc/motd`; echo "int motd_lines = $n;" > foo.h.new cmp -s foo.h foo.h.new 2> /dev/null || mv foo.h.new foo.h looks like: # filemon version 4 # Target pid 24291 V 4 E 29676 /bin/sh R 29676 /etc/ld.so.conf R 29676 /lib/libedit.so.2 R 29676 /lib/libterminfo.so.1 R 29676 /lib/libc.so.12 F 29676 4899 E 4899 /usr/bin/wc R 4899 /etc/ld.so.conf R 4899 /usr/lib/libc.so.12 R 4899 /etc/motd X 4899 0 W 29676 foo.h.new X 29676 0 # Bye bye E 3250 /bin/sh R 3250 /etc/ld.so.conf R 3250 /lib/libedit.so.2 R 3250 /lib/libterminfo.so.1 R 3250 /lib/libc.so.12 W 26673 /dev/null E 26673 /usr/bin/cmp R 26673 /etc/ld.so.conf R 26673 /usr/lib/libc.so.12 X 26673 2 E 576 /bin/mv R 576 /etc/ld.so.conf R 576 /lib/libc.so.12 M 576 'foo.h.new' 'foo.h' X 576 0 X 3250 0 # Bye bye Most records follow the format: type pid data where type is one of the list below, and unless otherwise specified, data is a pathname. C chdir(2). D unlink(2). E exec(3). F fork(2), vfork(2); data is the process id of the child. L link(2), symlink(2); data is two pathnames. M rename(2); data is two pathnames. R open(2) for read or read-write. W open(2) for writing or read-write. X exit(3); data is the exit status. V indicates the version of filemon. A filemon instance is created by opening /dev/filemon. Then use ioctl(filemon_fd, FILEMON_SET_PID, &pid) to identify the target process to monitor, and ioctl(filemon_fd, FILEMON_SET_FD, &output_fd) to direct the event log to an already-opened output file.
FILES
/dev/filemon
EXAMPLES
The following example demonstrates the basic usage of filemon: #include <filemon.h> pid_t pid; int filemon_fd, temp_fd; int status; filemon_fd = open("/dev/filemon", O_RDWR); temp_fd = mkstemp("/tmp/filemon.XXXXXXX"); /* give filemon the temp file to use */ ioctl(filemon_fd, FILEMON_SET_FD, &temp_fd); /* children do not need these once they exec */ fcntl(filemon_fd, F_SETFD, FD_CLOEXEC); fcntl(temp_fd, F_SETFD, FD_CLOEXEC); pid = fork(); switch(pid) { case -1: err(1, "cannot fork"); break; case 0: pid = getpid(); /* tell filemon to monitor this process */ ioctl(filemon_fd, FILEMON_SET_PID, &pid); execvp(...); _exit(1); break; default: status = wait(); close(filemon_fd); lseek(temp_fd, SEEK_SET, 0); /* read the captured syscalls from temp_fd */ close(temp_fd); break; } The output of filemon is intended to be simple to parse. It is possible to achieve almost equivalent results with dtrace(1) though on many sys- tems this requires elevated privileges. Also, ktrace(1) can capture sim- ilar data, but records failed system calls as well as successful, and is thus more complex to post-process.
HISTORY
filemon was contributed by Juniper Networks.
SECURITY CONSIDERATIONS
If the monitored process exits, and its pid gets reused, filemon will continue to report events for the new process (and its descendants) with- out any authorization checks. Monitoring of a process enables the target process to write to the track- ing process's file descriptor.
RESTRICTIONS
The filemon facility can only be used to track processes running in the system's native emulation. Neither processes using any of the COMPAT_xxx compatibility layers nor any descendants of such processes can be tracked. If two processes are monitored, and one is a descendant of the other, events related to the descendant process and its further descendants are delivered only to the descendant process's monitor. If a process is being monitored by two instances of filemon, events will be delivered only to the first instance created (when /dev/filemon was opened), regardless of the order in which the monitoring processes called ioctl(fd, FILEMON_SET_PID, pid). NetBSD 9.0 January 6, 2016 NetBSD 9.0
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