File system events mac os x

An individual log file can span multiple days depending on how much activity was occurring on the volume. System updates, upgrades, and application installs tend to generate a large number of FSEvents. Therefore, the last Event ID within this file is , which is 1 less than , FSEvent records are initially stored in memory.

When a change occurs to an object on a volume, the FSEvents API checks to see if the object has already been assigned an Event ID using the relative full path of the object. If no event ID has been assigned for the object in memory, one will be assigned to it and the relative full path of the object, the record flags, and the event ID will be stored in memory.

If the object was already assigned an event ID, the API will update the record flags to include the current change. For each subsequent change that the object incurs while it has been assigned an event ID in memory, the API coalesces the changes the record flags and stores it as a single event for the object. Once flushed to disk, the API will not modify the contents of the logs.

Find Log Files on Disk

The event record for the text file when parsed might look something like the following:. These limitations are the result of the lack of granularity imposed by the FSEvents API when recording changes and not the result of parsing what was recorded. FSEvent logs are stored as compressed archive files in gzip format.

Once the files are uncompressed they can be opened using a hex editor so that raw strings can be viewed. Each FSEvent log contains records that represent historical changes to objects on a volume. Each record within an FSEvent log consists of three major components:. They bear no relation to any particular clock or timebase. However, it can have multiple Event IDs across multiple logs.

It is the File System object inode number. This structure applies to MacOS Thanks go out to Joachim Metz for pointing that out. There can be multiple page headers in one FSEvents log. Following each page header is the start of a Record Full Path of an event.


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In the figure below, there are three events in total but only the first will be discussed. For the first event in our example this is located at offset 0x1a. The Event ID for this record is 0xd or 87, in decimal. Decoding record flags will not be covered in great detail but for this event the hex value of 0x indicates that this is a file that has been created, modified, finder information changed, and inode metadata changed. Note that there can be instances where the fullpath is not reported for an event. It is currently unknown why. An example of this is shown in the above example as the first event.

When the parser has finished parsing, the tab delimited file can by opened using Excel. FSEvent records are stored in the log in alphabetical order using the record full path filename column in the screenshot below. Keep in mind however that the chronological order relates only to when the first change occurred to an object. The FSEventsParser script also produces an SQLite database containing parsed records which is useful for times when parsed records can be in excess of 1 million.

File System Events | Apple Developer Documentation

The SQLite database also comes in handy when running queries to narrow down the records of interest. Events listed here only scratch the surface of what can be found in FSEvents logs. This section is provided to give you an idea of what can be found within those logs.

Interpreting the exact cause as to how these events were generated requires additional testing and validation. The image below shows files and folders that were sent to the Trash. We can query the SQLite database to get a list of approximate dates that the system was booted. This can include documents, downloads, and desktop activity. In the image below, a folder was renamed and two DMGs were created on the Desktop. In the Downloads directory, a ZIP file was created. Note that the creation of some of these files was initiated by the user me , and some were created by an application or the OS.

File System Events Programming Guide

In the Downloads directory,. When a drive is plugged in, the OS will try to mount it. Mounts are also recorded within FSEvents. Web browsers such as Safari and Chrome store website addresses or URLs in the name of a files associated with internet activity. The changes to those files are recorded in FSEvents. Most of the websites listed in the image below were the result of me directly visiting the site, others appear to have been from third party sites not directly visited.

The offset is equal to 0x So far, I discussed the key technical details regarding how to monitor the dylib loading event. After launching Safari and Wireshark, we can see that my tool can monitor the dylib loading event very well. In this blog, we discussed the key technical details regarding how to monitor file system events and dylib loading events using MACF. It is very useful for monitoring malicious behaviors of malware on macOS.

System Events: What Is It?

The other significant behavior of malware is network activity. In the next blog I will discuss how to monitor network activities udp, tcp, DNS query and response, etc. By Kai Lu March 30, Monitor File System Events The tool I developed can monitor all common file system events, including file open, read, write, rename, and delete operations. Figure 1. The operations related to file system events.

Figure 2. Figure 3. The implementation of the callback deleteFileHook is shown next. Figure 4.


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  • Monitoring macOS, Part II: Monitoring File System Events and Dylib Loading via MACF.
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  • The code snippet of the callback deleteFileHook. Figure 5. Figure 6. A code snippet of obtaining the full path of original file. Figure 7. A code snippet of obtaining the destination path of file. Figure 8. The definition of structure componen tname. Finally, I show the tool for monitoring file system events on macOS. Figure 9. The output of monitoring file delete event.

    Figure The ouput of monitoring file rename event.

    Monitor Dylib Loading Event The dynamic loader, dyld is designed to dynamically link and load the dynamic libraries on the macOS platform. The function mapSegments. The definition of function xmmap. The function dylibloadHook. The definition of structure fileglob. The output of monitoring dylib loading event. Conclusion In this blog, we discussed the key technical details regarding how to monitor file system events and dylib loading events using MACF. You are invited to stay tuned! References 1. Tags: fortiguard labs , malware , threat research , Mac OS , mac os x. Related Posts.