一、logcat對日志過濾
1.# logcat --help
# logcat --help Usage: logcat [options] [filterspecs] options include: -s Set default filter to silent. Like specifying filterspec '*:s' -f <filename> Log to file. Default to stdout -r [<kbytes>] Rotate log every kbytes. (16 if unspecified). Requires -f -n <count> Sets max number of rotated logs to <count>, default 4 -v <format> Sets the log print format, where <format> is one of: brief process tag thread raw time threadtime long -c clear (flush) the entire log and exit -d dump the log and then exit (don't block) -t <count> print only the most recent <count> lines (implies -d) -t '<time>' print most recent lines since specified time (implies -d) -T <count> print only the most recent <count> lines (does not imply -d) -T '<time>' print most recent lines since specified time (not imply -d) count is pure numerical, time is 'MM-DD hh:mm:ss.mmm' -g get the size of the log's ring buffer and exit -b <buffer> Request alternate ring buffer, 'main', 'system', 'radio', 'events', 'crash' or 'all'. Multiple -b parameters are allowed and results are interleaved. The default is -b main -b system -b crash. -B output the log in binary. -S output statistics. -G <size> set size of log ring buffer, may suffix with K or M. -p print prune white and ~black list. Service is specified as UID, UID/PID or /PID. Weighed for quicker pruning if prefix with ~, otherwise weighed for longevity if unadorned. All other pruning activity is oldest first. Special case ~! represents an automatic quicker pruning for the noisiest UID as determined by the current statistics. -P '<list> ...' set prune white and ~black list, using same format as printed above. Must be quoted. filterspecs are a series of <tag>[:priority] where <tag> is a log component tag (or * for all) and priority is: V Verbose （優先級最低） D Debug I Info W Warn E Error F Fatal S Silent (supress all output) （最高優先級，不會打印任何內容） '*' means '*:d' and <tag> by itself means <tag>:v If not specified on the commandline, filterspec is set from ANDROID_LOG_TAGS. If no filterspec is found, filter defaults to '*:I' If not specified with -v, format is set from ANDROID_PRINTF_LOG or defaults to "brief"
1. logcat命令位置：/system/bin/logcat
2.logcat的常用用法
# logcat *:W 過濾日志則會將該級別及以上的日志輸出
# logcat ActivityManager:I MyApp:D *:S 表示輸出tag=“ActivityManager”的Info以上級別日志，輸出tag=“MyApp”的Debug以上級別日志，及其它tag的Silent級別日志（即屏蔽其它 tag 日志）。
# logcat -d logcat應該是動態打印的，加-d后打印完log后退出，不阻塞
# logcat -t 20 只打印最近的20行log，-T也是類似的功能，但是打印完后不退出。
# logcat -f a.txt -f保存到文件中，不使用重定向符號的
# logcat | grep -i myapp 忽略大小寫。
# logcat | grep --color=auto -i priv-app 匹配到的“priv-app”會顯示出顏色
# logcat | grep --color=auto 1979 只打印出進程PID為1979的log
# logcat -c && logcat
# logcat -v time 打印時加上時間
# logcat -g 打印各個環形緩沖區的大小后退出
# logcat -S 打印出統計信息
# logcat | grep -E "Theft|u-blox" grep -E 正則表達式,可以一次性檢索多個關鍵字
# logcat <tag1>:<priority1> <tag2>:<priority2> 過濾低優先級的日志
# logcat *:E 只查看錯誤打印
3.有 3 種方式使用 logcat 打印日志：
可以通過 IDE(比如 Android Studio)提供的 logcat 窗口查看打印的日志
可以通過 adb 命令使用 logcat 在本地計算機進行日志查看
通過 adb 命令進入模擬器或者所連設備的 shell 命令窗口，進行 logcat 的操作和使用
4.設置輸出日志等級
通過設置優先級，過濾掉低優先級的日志，使用方式如: adb logcat <tag1>:<priority1> <tag2>:<priority2>
示例: logcat PowerManagerService:I PackageManager:I 表示logcat時不打印PowerManagerService和PackageManager的優先級低於Info的log
5.logcat選擇打印的緩沖區：
# logcat -b <buffer> 可以指定要打印的環緩沖區，“main”，“system”，“radio”或“events”。 允許多個-b連用，這樣打印的結果是交錯的，默認為: -b main -b system -b crash。
radio - 查看緩沖區的相關的信息.
events - 查看和事件相關的的緩沖區.
main - 查看主要的日志緩沖區.
system - 與系統相關的日志信息.
6. logcat默認的幾種輸出格式為
格式：logcat -v threadtime
(1)brief格式為：<priority>/<tag>(<pid>): <message> eg: D/HeadsetStateMachine( 1785): Disconnected process message: 10, size: 0
(2)process格式為：<priority>(<pid>) <message> eg: D( 1785) Disconnected process message: 10, size: 0 (HeadsetStateMachine)
(3)tag格式為：<priority>/<tag>: <message> eg: D/HeadsetStateMachine: Disconnected process message: 10, size: 0
(4)raw格式為：<message> eg: Disconnected process message: 10, size: 0
(5)time格式為：<datetime> <priority>/<tag>(<pid>): <message> eg: 08-28 22:39:39.974 D/HeadsetStateMachine( 1785): Disconnected process message: 10, size: 0
(6)threadtime格式為：<datetime> <pid> <tid> <priority> <tag>: <message> eg: 08-28 22:39:39.974 1785 1832 D HeadsetStateMachine: Disconnected process message: 10, size: 0
(7)long格式為：[ <datetime> <pid>:<tid> <priority>/<tag> ] <message> eg: [ 08-28 22:39:39.974 1785: 1832 D/HeadsetStateMachine ] Disconnected process message: 10, size: 0
二、日志打印函數
1.程序中使用ALOGx(),SLOGx(),RLOGx()來分別打印app,system,radio的log,
x表示下面6種打印級別：
V Verbose
D Debug
I Info
W Warn
E Error
F Fatal
比如：
#define LOG_TAG "LedHal"
ALOGI("hal_led_ioctl called: which=%d, status=%d", which, status);
打印如下：
I/LedHal ( 2284): hal_led_ioctl called: which=0, status=0 //打印等級/Tag (PID): message
三、日志統計
1.# logcat -b all -S 可以統計出各個log buffer中最健談的log的進程、UID、TAG
# logcat -b all -S size/num main radio events system crash stats performance security kernel Total Total 4294940/52209 1224624/6903 386275/3669 1197331/12884 165/3 0/0 9132/180 0/0 0/0 7112467/75848 Now 261517/3561 257987/1383 252696/2824 246225/2728 165/3 9132/180 1027722/10679 Logspan 1:09:38.987(3.9%) 2:15:44.731(24.2%) 2:15:41.166(96.9%) 2:15:44.791(37%) 3:03.21 2:10:35.716 2:15:48.058 Overhead 460933 335435 410840 398993 333 19212 1775074 update time=0, report time=0, buffer rate = 0 Byte/sec, log rate = 0 sec-1 buffer chatty rate = 15000 Byte/sec, log chatty rate = 100 sec-1 最健談的main log： Chattiest UIDs in main log buffer: Size +/- Pruned UID PACKAGE BYTES NUM 10061 com.android.systemui 51486 -14% 1256 1000 system 40438 -67% 3478 PID/UID COMMAND LINE " " 1612/1000 system_server 5384 2409 2972/1000 com.coloros.persist.system 2999 623 最健談的main log： Chattiest UIDs in radio log buffer: Size +/- Pruned UID PACKAGE BYTES NUM 1001 radio 246546 -3.6% 5766 1000 system 11037 5.2X 最健談的event log： Chattiest UIDs in events log buffer: Size +/- Pruned UID PACKAGE BYTES NUM 1000 system 231850 +4.3% 260 PID/UID COMMAND LINE " " 1612/1000 system_server 153760 14 最健談的system log： Chattiest UIDs in system log buffer: Size +/- Pruned UID PACKAGE BYTES NUM 1000 system 180236 -20% 8572 PID/UID COMMAND LINE " " 1612/1000 system_server 69620 8238 2972/1000 com.coloros.persist.system 68819 324 最健談的crash log： Chattiest UIDs in crash log buffer: Size UID PACKAGE BYTES 0 root 165 最健談的performance log： Chattiest UIDs in performance log buffer: Size UID PACKAGE BYTES 1000 system 2909 PID/UID COMMAND LINE " 1612/1000 system_server 556 最健談的PID: Chattiest PIDs: Size Pruned PID/UID COMMAND LINE BYTES NUM 2904/1001 com.android.phone 270946 5604 1612/1000 system_server 240357 10661 最健談的TID: Chattiest TIDs: Size Pruned TID/UID COMM BYTES NUM 2904/1001 com.android.phone 217685 4117 1765/1000 android.bg 78212 147 最健談的events log中的TAG: Chattiest events log buffer TAGs: Size Prune TAG/UID TAGNAME BYTES NUM 1003 auditd 89160 390 30047/1000 am_pss 73004 最健談的TAG： Chattiest TAGs: Size TID/PID/UID LOG_TAG NAME BYTES 2904/1001 SST 121294 auditd 89160