![]() These are logs of the log files, written by logd as it performs its log file maintenance. Of the other files written into the log folders, by far the most interesting and accessible are those named logdata.statistics.0.txt and similar. To get a full view of log entries for a given period, it would thus be necessary to view both the Persist and Special log files covering that period, when browsing them individually, such as in a logarchive. However, the log command and Consolation also allow you to browse individual log files, in which case only those from the selected log file are shown. When you use Console, Consolation or log to view live log entries (streamed live via diagnosticd, or historic entries in the current system log), those shown merge entries from the Persist and Special log files. They vary more widely in period and size, and their coverage may not be continuous. Special log files are named using similar hexadecimal numbers, but appear to reuse recent numbers as well. Persist log files are named using hexadecimal numbers in sequence, starting from acev3 when that Mac is first started up in Sierra or later, and switching to a new log file when there is around 10.5 MB of data in the current file, although rotation occurs at irregular intervals, so the time periods and sizes vary. Persist files are kept intact until they reach an age of about twenty days, or more, when they are simply deleted during log file rotation. Older Special log files thus get progressively smaller as they age, until they contain almost nothing, and are automatically deleted. However, Special log files are weeded over time to ‘compress’ them, which is one of logd‘s functions. It’s not immediately clear why the log separates entries into Persist and Special log files, as they both contain entries of the same types. Another daemon involved is diagnosticd, which can feed a live log stream such as that viewed in Apple’s Console utility, or in the log stream command. Periodically it rotates log files, and weeds the entries in those deemed Special until they are eventually reduced to nothing and removed. Logs are managed by a background daemon logd, which is undocumented but responsible for compressing and writing log entries, and for maintaining the log files. ![]() There is another folder named dsc which contains similar files. These include crash events and other items which overflow single line entries in the log. var/db/uuidtext/ contains a series of folders, named 00 to FF, each containing files named by UUID for specific log events, which extend beyond normal log entries. Other data files such as shutdown.log containing predominantly plain text details of significant log events.A series of plain text files named logdata.statistics.0.txt and others in numeric sequence – the log logs.These contain binary data about time synchronisation between log events and the high-resolution Mach system clock. The folder timesync, which contains timesync files numbered in order, extending back to the Sierra upgrade over a year ago.The folder Special, which contains additional tracev3 files holding supplementary log content.The folder Persist, which contains the main tracev3 files for the log as saved to disk.Other folders in /var/db/diagnostics/ and /var/db/uuidtext/ contain ancillary information for those logs. Log contents are stored as tracev3 files – an undocumented compressed binary format – in /var/db/diagnostics/Persist/ and /var/db/diagnostics/Special/. As Apple’s team stated in their 2016 presentation “we want as much logging on all the time as possible”. More significant entries may be written into a system or console log, but there is no centralised log in which everything is recorded.Īpple’s grand design eliminates almost all other logs (macOS Server and some services still maintain their own, though), and fills a single unified log with many hundreds or thousands of log entries every minute. They’re easy to access, entries are relatively sparse, and they are separated into different voices: printing system errors and other log entries will normally go into one or more print logs, for example. Traditional logs, found on most conventional Unix systems, are a bunch of text files stored in several different folders. This article is a small step forward in understanding the unified log, which is used in iOS, watchOS, and tvOS too. Inevitably, the focus at WWDC was on explaining to developers how to write to the new log, and precious little was revealed about the log itself. At the time, at WWDC in June 2016, it was all rather novel, and didn’t arrive until the release of macOS Sierra the following September (2016). ![]() It has been well over a year since Apple told us much about the new unified log which it introduced in Sierra, and continues in High Sierra. ![]()
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