How can I view and examine the Android log?

Question

There is a lot of interesting stuff in the Android system log, that is helpful in many ways

• find root causes of problems
• identify misbehaving apps

How can I view and examine the Android log?

Answer 1

You can either download the SDK and use adb logcat or get aLogcat from the Market, which shows the log directly on your phone.

Jelly Bean

With Android 4.1 (aka Jelly Bean) the full system log is only visible if you have root. Apps can only see their own log messages. For more information view see this question.

Answer 2

A found that CatLog displays the Android log a little bit better then aLogcat. Besides adb logcat, that's what I am using.

Answer 3

It is located in /sdcard/bugreports.

Answer 4

Log-File locations

There are several directories where logs (including those from crashes) might appear -- not all of them are standardized (i.e. some may be ROM-specific).

• /data/anr: Some trace files seem to get here (Dalvik writes stack traces here on ANR, i.e. "Application Not Responding" aka "Force-Close"; see e.g. log excerpts here)
• /data/dontpanic seems to be a standard location (AOSP), and contains some crash logs including traces (see e.g. viaForensics and StackOverflow)
• /data/kernelpanics is another location -- not having had any "kernel panic" on my Android devices, I saw no content there yet.
• the /data/panic/panic_daemon.config may point to other locations configured -- on my Droid 2 it mentions /sdcard/panic_data/
• mentioned Droid 2 also has a /data/panicreports directory (empty here)
• /data/tombstones may hold several tombstone_nn files (with nn being a serial, increased with every new file). As tombstones are placed for the dead, it is done here for "processes died by accident" (i.e. crashed) -- and it is what is referred to as "core dumps" on Linux/Unix systems. However, not all apps create tombstones; this must be explicitly enabled by the developer (see Debugging Android Core Dumps).

There may be some more locations which escaped me; but as most logging is done on tmpfs, these data are lost with a reboot, and would not match the OPs question.

Log commands to use with a terminal app (or adb)

Several commands can get you tons of information. For most of them, it is to recommend to re-direct them to a file (> filename.ext) or pipe them through a filter (| grep search-for-this):

Kernel log

The following works without root:

$ dmesg
<6>[82839.126586] PM: Syncing filesystems ... done.
<7>[82839.189056] PM: Preparing system for mem sleep
<4>[82839.189361] Freezing user space processes ... (elapsed 0.05 seconds) done.
<4>[82839.240661] Freezing remaining freezable tasks ... (elapsed 0.00 seconds) done.
<snip>

Logcat

Here you can e.g. specify what area you are interested in -- radio, events...

# logcat -b events
I/am_create_service( 3457): [1085416560,nitro.phonestats/.widget.WidgetProvider4x1$WidgetUpdateService4x1,,3721]
I/am_destroy_service( 3457): [1085416560,nitro.phonestats/.widget.WidgetProvider4x1$WidgetUpdateService4x1,3721]
I/notification_cancel( 3457): [nitro.phonestats,4,0] 
<snip>

Getting device info

And tons of it: Device specifics, account information, services...

$ dumpsys
Currently running services:
  LocationProxyService
  SurfaceFlinger
  accessibility
  account
  activity
<snip>
DUMP OF SERVICE account:
Accounts:
  1 Account {name=xxxxxxx@googlemail.com, type=com.google}
<snip> 

$ dumpstate
========================================================
== dumpstate: 2012-08-18 23:39:53
========================================================

Build: Gingerbread GWK74 - CyanogenMilestone2
Bootloader: 0x0000
Radio: unknown 
<snip>
------ MEMORY INFO (/proc/meminfo) ------
MemTotal: 487344 kB
MemFree: 10436 kB 
<snip>

All-in-One

Make a big ball with everything together, from logcat to dumpstate:

$ bugreport > /mnt/sdcard/bugreport.txt

I'm pretty sure you really want to redirect that last command... xD

Something about permissions

P.S.: Naturally, access to those information may require root, as most of the sources are located on internal storage.

Answer 5

Free app SysInfo (Project Page) will display the system logs as well as zip a complete system report to send via email, dropbox, NFC, etc. Not to mention lots of other interesting system information.