Android的logcat日志详解

Android log系统

logcat介绍

logcat是android中的一个命令行工具，可以用于得到程序的log信息。下面介绍 adb logcat中的详细参数命令以及如何才能高效的打印日志，或把日志保存到我们指定的位置。

可以输入 adb logcat --help，查看一下一些简单的数据格式：

adb logcat --help

输出结果：

Usage: logcat [options] [filterspecs]

General options:
  -b, --buffer=<buffer>       Request alternate ring buffer(s):
                                main system radio events crash default all
                              Additionally, 'kernel' for userdebug and eng builds, and
                              'security' for Device Owner installations.
                              Multiple -b parameters or comma separated list of buffers are
                              allowed. Buffers are interleaved.
                              Default -b main,system,crash,kernel.
  -L, --last                  Dump logs from prior to last reboot from pstore.
  -c, --clear                 Clear (flush) the entire log and exit.
                              if -f is specified, clear the specified file and its related rotated
                              log files instead.
                              if -L is specified, clear pstore log instead.
  -d                          Dump the log and then exit (don't block).
  --pid=<pid>                 Only print logs from the given pid.
  --wrap                      Sleep for 2 hours or when buffer about to wrap whichever
                              comes first. Improves efficiency of polling by providing
                              an about-to-wrap wakeup.

Formatting:
  -v, --format=<format>       Sets log print format verb and adverbs, where <format> is one of:
                                brief help long process raw tag thread threadtime time
                              Modifying adverbs can be added:
                                color descriptive epoch monotonic printable uid usec UTC year zone
                              Multiple -v parameters or comma separated list of format and format
                              modifiers are allowed.
  -D, --dividers              Print dividers between each log buffer.
  -B, --binary                Output the log in binary.

Outfile files:
  -f, --file=<file>           Log to file instead of stdout.
  -r, --rotate-kbytes=<n>     Rotate log every <n> kbytes. Requires -f option.
  -n, --rotate-count=<count>  Sets max number of rotated logs to <count>, default 4.
  --id=<id>                   If the signature <id> for logging to file changes, then clear the
                              associated files and continue.

Logd control:
 These options send a control message to the logd daemon on device, print its return message if
 applicable, then exit. They are incompatible with -L, as these attributes do not apply to pstore.
  -g, --buffer-size           Get the size of the ring buffers within logd.
  -G, --buffer-size=<size>    Set size of a ring buffer in logd. May suffix with K or M.
                              This can individually control each buffer's size with -b.
  -S, --statistics            Output statistics.
                              --pid can be used to provide pid specific stats.
  -p, --prune                 Print prune rules. Each rule is specified as UID, UID/PID or /PID. A
                              '~' prefix indicates that elements matching the rule should be pruned
                              with higher priority otherwise they're pruned with lower priority. All
                              other pruning activity is oldest first. Special case ~! represents an
                              automatic pruning for the noisiest UID as determined by the current
                              statistics.  Special case ~1000/! represents pruning of the worst PID
                              within AID_SYSTEM when AID_SYSTEM is the noisiest UID.
  -P, --prune='<list> ...'    Set prune rules, using same format as listed above. Must be quoted.

Filtering:
  -s                          Set default filter to silent. Equivalent to filterspec '*:S'
  -e, --regex=<expr>          Only print lines where the log message matches <expr> where <expr> is
                              an ECMAScript regular expression.
  -m, --max-count=<count>     Quit after printing <count> lines. This is meant to be paired with
                              --regex, but will work on its own.
  --print                     This option is only applicable when --regex is set and only useful if
                              --max-count is also provided.
                              With --print, logcat will print all messages even if they do not
                              match the regex. Logcat will quit after printing the max-count number
                              of lines that match the regex.
  -t <count>                  Print only the most recent <count> lines (implies -d).
  -t '<time>'                 Print the lines since specified time (implies -d).
  -T <count>                  Print only the most recent <count> lines (does not imply -d).
  -T '<time>'                 Print the lines since specified time (not imply -d).
                              count is pure numerical, time is 'MM-DD hh:mm:ss.mmm...'
                              'YYYY-MM-DD hh:mm:ss.mmm...' or 'sssss.mmm...' format.
  --uid=<uids>                Only display log messages from UIDs present in the comma separate list
                              <uids>. No name look-up is performed, so UIDs must be provided as
                              numeric values. This option is only useful for the 'root', 'log', and
                              'system' users since only those users can view logs from other users.

filterspecs are a series of
  <tag>[:priority]

where <tag> is a log component tag (or * for all) and priority is:
  V    Verbose (default for <tag>)
  D    Debug (default for '*')
  I    Info
  W    Warn
  E    Error
  F    Fatal
  S    Silent (suppress all output)

'*' by itself means '*:D' and <tag> by itself means <tag>:V.
If no '*' filterspec or -s on command line, all filter defaults to '*:V'.
eg: '*:S <tag>' prints only <tag>, '<tag>:S' suppresses all <tag> log messages.

If not specified on the command line, filterspec is set from ANDROID_LOG_TAGS.

If not specified with -v on command line, format is set from ANDROID_PRINTF_LOG
or defaults to "threadtime"

log类是一个日志类，可以在代码中使用logcat打印出消息。常见的日志记录方法包括。

例如：

// 开发过程中获取 log
Log.i("MyActivity","MyClass.getView() - get item number"+position);
//adb 获取 log
adb logcat
adb logcat 输出的⽇志格式如下：
I/ActivityManager( 1754): Waited long enough for: ServiceRecord{2b24178c u0
com.google.android.gms/.checkin.CheckinService}

logcat命令格式

语法格式：

[adb] logcat [] … [ ] …
PC 端使⽤： adb logcat
shell 模式下使⽤： logcat

logcat缓冲区

缓冲区介绍

Android 日志系统为日志消息保留了多个环形缓冲区，但并非多有的日志消息都会发送到默认的环形缓冲区。这里可以采用 logcat -b 命令查看设备的其他缓冲区：

缓冲区模型

logcat命令参数

⼀般⻓时间输出 log 的话建议 -f ， -n ， -r 三个参数连⽤，这样当⼀个⽂件⽇志输出满了之后可以⻢上在另⼀个中进⾏输出。

Android 日志系统为日志消息保留了多个环形缓冲区，但并非多有的日志消息都会发送到默认的环形缓冲区。

logcat -b 是 logcat 命令的一个选项，用于指定查看日志缓冲区。你可以用它来查看不同类型的日志缓冲区。下面是基本用法：

logcat -b events|grep -E "am_proc_start|input_focus.*entering"

基本命令格式：

shCopy Code
adb logcat -b <buffer>

选项说明：

• main: 默认缓冲区，包含大多数应用程序和系统日志。

• system: 系统日志缓冲区，包含系统服务和硬件相关日志。

• events: 事件日志缓冲区，记录系统事件和调试信息。

• crash: 崩溃日志缓冲区，记录应用崩溃的信息。

示例用法：

• 查看主缓冲区日志：

shCopy Code
adb logcat -b main

• 查看系统缓冲区日志：

shCopy Code
adb logcat -b system

• 查看事件缓冲区日志：

shCopy Code
adb logcat -b events

• 查看崩溃缓冲区日志：

shCopy Code
adb logcat -b crash

这些选项帮助你根据需要过滤和查看不同类型的日志数据。

logcat格式化输出

参数说明

⽇志消息包含⼀个元数据字段，除了标签和优先级，您可以修改输出显示⼀个特定的元数据字段格式的消息。为此，您使⽤-v 选项来指定⼀个⽀持的输出格式。⼀下为⽀持的格式：

当 logcat 开始，指定想要输出格式 -v 选项：

[adb] logcat [-v ]
adb logcat –v thread

只能指定⼀个输出格式 -v。

logcat优先级

按日志级别过滤日志：

adb logcat <tag>[:priority]

tag 表示标签；priority 表示输出级别；

日志默认级别是 V，如果错误日志我们选择 E 就可以，Android 的日志分为如下几个优先级（priority）：

*可以是某个tag，如果没有指明，就表示所有。