TweetFollow Us on Twitter

Mac In The Shell -- Which Log?

Volume Number: 23 (2007)
Issue Number: 03
Column Tag: Mac in the Shell

Mac In The Shell -- Which Log?

Following up on which log shows you what

by Edward Marczak


I've had incredible response to my last two columns that talked about logs: what they are, how to interpret them and how to notify yourself if a log is telling you something important. More than any other question, however, people have asked, "which log does what? While I gave an overview of some logs, there are plenty more that I haven't gone into, and more locations for logs than I could describe previously. That's what I'll be following up on this month. So, read on for even more on logs.

Kinda I Want To

Just as a review for anyone who didn't read the previous columns, logs are text files that running programs write to that keep track of their activity. Text files, that's all. (OK, an app could keep a binary log, but for the most part, text it is). This allows other apps and, more importantly, humans to read their contents. Apps are free to deal with logging on their own, or, they can use syslog to hand off their data to the system logger. It's a bit of a style issue, and usage is roughly split on which method is chosen. There's nothing that says that an application can't do both. Let's look quickly again at the syslog method.

The system logger, aka "syslog, is a daemon run at boot that should be running all of the time. It listens for logging data locally, and knows where to put a logging entry based on its configuration file /etc/syslog.conf. "syslogd can also be setup to listen for logging data from other machines as well. Log data can be categorized by facility and level (a "selector). The facility is basically where the data is coming from ("mail, "ftp, etc., along with some generic facilities). The level describes the severity of the log message. The currently defined levels are:

Emergency (level 0) Alert (level 1) Critical (level 2) Error (level 3) Warning (level 4) Notice (level 5) Info (level 6) Debug (level 7)

(Don't you love it when things neatly fit into a byte?) Looking at /etc/syslog.conf, you can then see which messages will be directed to which files. Note that some will go to multiple files.

This is a bit of a review, as all of this (and more) was covered in previous articles in this column.

Down In It

Apple has created a little bit of a split with logging: "Unix-y files in /var/log, and everything else. While that may be a bit of an overgeneralization, it's a good general guideline.

syslogd, as you can see from /etc/syslog.conf, will dump just about everything in some log residing in /var/log. Additionally, several non-syslog sending services also drop their files somewhere into the /var/log hierarchy. The two big notables in this category would be apache logging into /var/httpd and samba, which logs into /var/samba. You'll also find some other non-syslog-ish files hanging around in /var/log, and we'll address those a little later.

The other place you'll find good logging information falls into the "everything else category. You'll find these in /Library/Logs or ~/Library/Logs. System processes will log to /Library/Logs and user processes, when the user home directory is writable, will log to ~/Library/Logs. For example, anything that needs admin level rights to run AFP logs, Software Update and, my favorite, Directory Services will log to the System directory /Library/Logs. Other user-space apps Logic, SyncServices, Parallels, etc. will log into the user's own Library/Logs.

If you've peeked into either of these directories, you'll notice that there's another category of logs: logs that get generated as the result of a crash.

Something I Can Never Have

For those of you obsessed with the running process list, you'll no doubt have noticed the persistent /usr/libexec/crashreporterd. Apple's crash reporter daemon hangs around waiting for an application to crash. Technically, it listens for a Mach exception to be generated, and, upon that happening, launches crashdump. crashdump then logs and reports the event to the user. If the user can be determined, and they have a writable home, the report goes into ~/Library/Logs/CrashReporter. You really forget how much stuff takes a dive until you peek in there:

Jack-Kerouac:~/Library/Logs/CrashReporter marczak$ ls -1
Now Up-To-Date.crash.log
Workgroup Manager.crash.log

Wow. When an app's owner can't be determined, is a system process, or the user's home directory is not writeable, crashdump logs into /Library/Logs:

Jack-Kerouac:/Library/Logs/CrashReporter root# ls -1 
Exited process.crash.log

LoginWindow crash...I like that one! crashreporter itself, however, logs its actions into /var/log/crashreporter.log. Finally, crashreporterd is also responsible for writing panic logs when the system is rebooted after a panic find the log at /Library/Logs/panic.log.

Terrible Lie

If you root around /var/log long enough, you'll even start to notice some other files that aren't syslog generated at all. The most notable of the bunch are daily.out, weekly.out and monthly.out. These log files are generated by the daily, weekly and monthly periodic jobs that run overnight (if your machine is up and running, but not necessarily logged in).

Also of note are wtmp and lastlog. Interestingly, these are binary log files, and must be read with another application. These are not present for troubleshooting per se, but instead track login activity. User IDs, along with their login time get written to lastlog. From there, the utmp file gets updated with the user login information, and the same utmp record gets written to /var/log/wtmp. users, w and who use utmp to provide their information, while last and ac use wtmp.

That's What I Get

So, back to the original question: which logs record which bit of information? Here's a 40,000 ft. view:


Along with asl.log, these are the big kahunas. Most system related activity is logged here. Specifically, the following selectors log to system.log:


As mentioned in January, asl.log pretty much gets everything, and displays the facility and level with the log message.


Messages from Apple's SecurityServer get logged here along with anything in the authpriv facility. Good one to keep an eye on. Interestingly, though, some security-related information logs to system log as well (such as sshd authentication errors through PAM).

/var/log/mail.log and /var/log/mailaccess.log

Complimentary logs that describe mail (if you're running OS X Server's built-in mail OS X client' also uses /var/log/mail.log). mail.log contains activity for postfix, SMTP sending and receiving while mailaccess.log contains cyrus' imap and pop activity. mail.log is the place to look when clients are telling you that they sent mail that the intended recipients never received (mail going out), or that someone sends them e-mail which they themselves never received (mail coming in).


Huge. HUGE I say! Anyone operating in an OD, AD or other LDAP-reliant environment should be checking here occasionally. Of course, if you're trying to bind a workstation to a directory, and it's just not working for some reason, this is the place to check. Don't forget to throw DirectoryService into debug mode (killall -USR1 DirectoryService, logging to DirectoryService.debug.log), or use boot-time debugging (touch /Library/Preferences/DirectoryService/.DSLogDebugAtStart which will also log to DirectoryService.debug.log) if the situation calls for it covered in detail in past Mac In The Shell articles.

Logs that you don't need explained

There are some logs that simply don't need any explanation. These include:

/var/log/ftp.log (contents of the ftp server)
/var/log/httpd/* (Apache's log files)
/var/log/samba/* (Samba's log files)
/var/log/lpr.log (lpr printing activity)
/var/log/cups/* (CUPS web sever activity)
/Library/Logs/Software Update.log (Software Update install history)

/Library/Logs/AppleFileService OK, perhaps this one does need some explanation. But not by me from the engineers at Apple. This should be the Mecca of information that you reach for when you want to track activity coming in through AFP. However, details in this log are so sparse to render it useless. Despite the fact that AppleFileServer runs as one grand, monolithic process, we need it to give up the goods on what's happening internally in these logs.

The mega-log

Remember, that you can always have all syslog messages be delivered to a single file by using a wildcard selector in /etc/syslog.conf:

*.*      /var/log/mega.log

…although asl.log is already catching most of that. Further remember that this will not capture everything else that is performing logging on its own and not using syslog/asl.

The Only Time

While I made a strong case for watching and examining logs using good ol Unix tools grep, tail and less and I would still make that assertion, there are some other very useful tools out there.

Figure 1: Splunk searching for events (detail) is the most obvious for us Mac users; it's "built-in and clearly Mac-like. I still think it's a miserable way to follow log activity as it happens, but it is a fantastic tool for exploring the various logs that exist on the system. Fire up (located in the Utilities folder) and poke around. It's a great learning experience.

I've found a newer tool on the market to also be very useful, and while it's not Mac-specific, it's nice that there's an OS X version at all. Splunk is billed as a logfile search engine. It comes in a free version that will sift through up to 500MB of logs per day, and a paid version which not only removes that restriction altogether, but also adds Splunk-to-Splunk logging for log correlation across many machines, and also authentication which is missing in the free version.

Splunk alone could take up an entire column (and may very well one day soon); it is so easy to get going, that I'd recommend the download. Excellent documentation exists on the site as well. Of course, Splunk makes it really easy to search for events, but I've found that it's a nice exploratory tool in general. Splunk quickly categorizes events and can let you filter on those events. Figure 1 shows the search engine, running in a browser, looking at event type 9 on my machine.

Even cooler, perhaps, is the ability to look at the frequency of events. Figure 2 shows the frequency of events that appear in the secure.log of my machine clearly a good one to keep an eye on and reign in this kind of data.

Figure 2 Splunk showing the frequency of various events that appear in a given source.

In a small-to-medium sized organization, you could set up a single server as a log host (check the prior logging articles for instructions) and have Splunk access that log. 500MB is a lot of logging information. Enough that you shouldn't have a problem using the free version of Splunk.


So here's the real story with logs: you can ignore them, sure. Then when a problem crops up, you can just tell your client/employer that this is just the way computers are. There are bugs, there are problems; such is life. If you watch the logs, you'll know there's a problem, and then you'll actually have to do something about it.

Or, you can realize that this is the only way the system can speak to you and more often that not, you're warned well in advance of any catastrophic problems. You can head these off at the pass. You can keep the system providing services without interruption and keep up with real work.

Of course, the unfortunate cases do arise where you need to ascertain what happened after the fact. Did that mail get sent? Did that volume bomb on space and then recover without us really knowing? Was someone trying to brute-force a login through ssh at the same time our web server was under attack? In those cases, knowing which logs to look in and how to read them are your only resource for piecing together information after an event took place.

Media of the month: you might suspect it would be some Nine Inch Nails title, however, I'd have to disappoint: that was only a passing fancy. The real Media of the Month is, "Innumeracy: Mathematical Illiteracy and Its Consequences by John Allen Paulos. A book that I forgot I had until I lent it out. Easy, enjoyable, powerful reading.

WWDC time again! Apple has announced the dates (June 11th through the 15th, if you'd missed it), so, get ready. If you're attending, I hope to see you there in person! Until then, though, I'll see you in print next month...

Ed Marczak owns and operates Radiotope, a technology consultancy that brings enterprise solutions to small and medium-sized businesses. Outside of this piece of the puzzle, he is Executive Editor of MacTech Magazine, a husband and father, and CTO of WheresSpot, among other things. Find the missing tech piece at .


Community Search:
MacTech Search:

Software Updates via MacUpdate

Gopogo guide - How to bounce like the be...
Nitrome just launched a new game and, as to be expected, it's a lot of addictive fun. It's called Gopogo, and it challenges you to hoparound a bunch of platforms, avoiding enemies and picking up shiny stuff. It's not easy though - just like the... | Read more »
Sago Mini Superhero (Education)
Sago Mini Superhero 1.0 Device: iOS Universal Category: Education Price: $2.99, Version: 1.0 (iTunes) Description: KAPOW! Jack the rabbit bursts into the sky as the Sago Mini Superhero! Fly with Jack as he lifts impossible weights,... | Read more »
Star Wars: Galaxy of Heroes guide - How...
Star Wars: Galaxy of Heroes is all about collecting heroes, powering them up, and using them together to defeat your foes. It's pretty straightforward stuff for the most part, but increasing your characters' stats can be a bit confusing because it... | Read more »
The best cooking apps (just in time for...
It’s that time of year again, where you’ll be gathering around the dinner table with your family and a huge feast in front of you. [Read more] | Read more »
Square Rave guide - How to grab those te...
Square Rave is an awesome little music-oriented puzzle game that smacks of games like Lumines, but with its own unique sense of gameplay. To help wrap your head around the game, keep the following tips and tricks in mind. [Read more] | Read more »
Snowboard Party 2 (Games)
Snowboard Party 2 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Crowned the best snowboarding game available on the market, Snowboard Party is back to fulfill all your adrenaline needs in... | Read more »
One Button Travel (Games)
One Button Travel 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: “To cut a long story short, If you like interactive fiction, just go buy this one.” - “Oozes the polish that... | Read more »
Light Apprentice Volume 1 (Games)
Light Apprentice Volume 1 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Light Apprentice Volume 1 includes Chapters 1 to 4, all gathered in a new exclusive game. When life in the world of... | Read more »
The best games like Animal Crossing on m...
Animal Crossing amiibo Festival is out right now for the Wii U, reminding us of just how much fun that world can be. Or at least to go back and check in on our villages once in a while. [Read more] | Read more »
Between 2 Taps - Tap for Tap interview M...
Hello, and welcome back to Between 2 Taps, Tap for Tap’s Indie Dev interview series. [Read more] | Read more »

Price Scanner via

iMobie Releases its Ace iOS Cleaner PhoneClea...
iMobie Inc. has announced the new update of PhoneClean 4, its iOS cleaner designed to reclaim wasted space on iPhone/iPad for use and keep the device fast. Alongside, iMobie hosts a 3-day giveaway of... Read more
Black Friday deals on the Apple Watch and App...
Apple resellers are offering discounts and bundles with the purchase of an Apple Watch this Black Friday weekend. Below is a roundup of the deals being offered by authorized Watch resellers: Apple... Read more
Early Black Friday sale at B&H Photo, up...
B&H Photo has all new Macs on sale for up to $500 off MSRP as part of their early Black Friday sale including free shipping plus NY sales tax only: - 15″ 2.2GHz Retina MacBook Pro: $1699 $300 off... Read more
NewerTech/OWC/MacSales Black Friday Deals 201... • Free Shipping available on nearly EVERYTHING on orders $35.00 & up within USA + • International Delivery Specials from $2.99+ Special Purolator... Read more
Walmart Black Friday deals: $100 off select i...
Walmart has released their Black Friday deals for 2015, now available online. Choose free shipping or free local store pickup (if available): - 16GB iPad Air 2: $399, $100 off MSRP - 16GB iPad Air: $... Read more
Photo Cleaner 1.0 Reclaims iPhone Storage Spa...
Seoul, Korea based mix1009 has announced the release and immediate availability of Photo Cleaner 1.0, their handy iPhone app that deletes the video portion of Live Photos, in order to reclaim space... Read more
Black Friday and Holiday sales on our price t...
Scan our Mac Price Trackers for the latest Black Friday and Holiday season information on sales, bundles, and availability on systems from Apple’s authorized internet/catalog resellers. We update the... Read more
Best Buy Black Friday deals: Up to $200 off M...
Best Buy has posted their Black Friday sale prices for 2015. Save on MacBook Pros, MacBooks, MacBook Airs, iMacs, iPads, and Apple Watches. Choose free shipping or free local store pickup (if... Read more
Save $30-$40 on new Apple TVs after rebate
Adorama has new Apple TVs on sale for up to $40 off MSRP after mail-in rebate, good through December 15th. Shipping is free, and Adorama charges NY & NJ sales tax only: - 32GB Apple TV: $119.99... Read more
13-Inch Haswell MacBook Air At Two Years – Th...
The 13-inch mid-2013 “Haswell” MacBook Air I ordered in Apple’s November 2013 Black Friday sale was my first new Mac in four and a half years — the longest interval I’ve gone between system upgrades... Read more

Jobs Board

Storefront Operations Coordinator, *Apple* -...
# Storefront Operations Coordinator, Apple -Latin America Job Number: 43587750 Miami, Florida, United States Posted: Oct. 16, 2015 Weekly Hours: 40.00 **Job Summary** The Read more
*Apple* Enterprise / Government Professional...
# Apple Enterprise / Gove ment Professional Services Engineer Job Number: 42292976 Reston, Virginia, United States Posted: Aug. 18, 2015 Weekly Hours: 40.00 **Job Read more
iOS Wallet & *Apple* Pay Engineer - App...
# iOS Wallet & Apple Pay Engineer Job Number: 40586801 Santa Clara Valley, Califo ia, United States Posted: Nov. 16, 2015 Weekly Hours: 40.00 **Job Summary** The iOS Read more
Software Engineer, *Apple* Watch - Clock Fa...
# Software Engineer, Apple Watch - Clock Face Team Job Number: 44368761 Santa Clara Valley, Califo ia, United States Posted: Nov. 14, 2015 Weekly Hours: 40.00 **Job Read more
Administrative Assistant, *Apple* Online St...
# Administrative Assistant, Apple Online Store Job Number: 43992352 Santa Clara Valley, Califo ia, United States Posted: Nov. 9, 2015 Weekly Hours: 40.00 **Job Summary** Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.