操作日志：
起因：Nexus 7 flo 华硕平板，刷了一个CWM Recovery之后变成了砖机；
尝试1：使用CWM Recovery清除数据，开机失败
尝试2：刷入CM 11 Snapshot的zip卡刷包，并使用Recovery清除数据，开机失败
尝试3：刷入CM 11 eng自己编译的版本，并使用Recovery清除数据，开机失败
尝试4：fastboot flash boot /path/to/boot.img，并刷入 CM 11 eng自己编译的版本，并Recovery清除数据，开机失败
尝试5：使用Logcat抓日志，输出如下
1 D/AndroidRuntime( 532): >>>>>> AndroidRuntime START com.android.internal.os.ZygoteInit <<<<<< 2 D/AndroidRuntime( 532): CheckJNI is ON 3 E/dalvikvm( 532): Could not stat dex cache directory '/data/dalvik-cache': No such file or directory 4 I/dalvikvm( 532): Unable to open or create cache for /system/framework/core.jar (/data/dalvik-cache/system@framework@core.jar@classes.dex) 5 D/dalvikvm( 532): Unable to process classpath element '/system/framework/core.jar' 6 E/dalvikvm( 532): Could not stat dex cache directory '/data/dalvik-cache': No such file or directory 7 I/dalvikvm( 532): Unable to open or create cache for /system/framework/conscrypt.jar (/data/dalvik-cache/system@framework@conscrypt.jar@classes.dex) 8 D/dalvikvm( 532): Unable to process classpath element '/system/framework/conscrypt.jar' 9 E/dalvikvm( 532): Could not stat dex cache directory '/data/dalvik-cache': No such file or directory 10 I/dalvikvm( 532): Unable to open or create cache for /system/framework/okhttp.jar (/data/dalvik-cache/system@framework@okhttp.jar@classes.dex) 11 D/dalvikvm( 532): Unable to process classpath element '/system/framework/okhttp.jar' 12 E/dalvikvm( 532): Could not stat dex cache directory '/data/dalvik-cache': No such file or directory 13 I/dalvikvm( 532): Unable to open or create cache for /system/framework/core-junit.jar (/data/dalvik-cache/system@framework@core-junit.jar@classes.dex) 14 D/dalvikvm( 532): Unable to process classpath element '/system/framework/core-junit.jar' 15 E/dalvikvm( 532): Could not stat dex cache directory '/data/dalvik-cache': No such file or directory 16 I/dalvikvm( 532): Unable to open or create cache for /system/framework/bouncycastle.jar (/data/dalvik-cache/system@framework@bouncycastle.jar@classes.dex) 17 D/dalvikvm( 532): Unable to process classpath element '/system/framework/bouncycastle.jar' 18 E/dalvikvm( 532): Could not stat dex cache directory '/data/dalvik-cache': No such file or directory 19 I/dalvikvm( 532): Unable to open or create cache for /system/framework/ext.jar (/data/dalvik-cache/system@framework@ext.jar@classes.dex) 20 D/dalvikvm( 532): Unable to process classpath element '/system/framework/ext.jar' 21 E/dalvikvm( 532): Could not stat dex cache directory '/data/dalvik-cache': No such file or directory 22 I/dalvikvm( 532): Unable to open or create cache for /system/framework/framework.jar (/data/dalvik-cache/system@framework@framework.jar@classes.dex) 23 D/dalvikvm( 532): Unable to process classpath element '/system/framework/framework.jar' 24 E/dalvikvm( 532): Could not stat dex cache directory '/data/dalvik-cache': No such file or directory 25 I/dalvikvm( 532): Unable to open or create cache for /system/framework/framework2.jar (/data/dalvik-cache/system@framework@framework2.jar@classes.dex) 26 D/dalvikvm( 532): Unable to process classpath element '/system/framework/framework2.jar' 27 E/dalvikvm( 532): Could not stat dex cache directory '/data/dalvik-cache': No such file or directory 28 I/dalvikvm( 532): Unable to open or create cache for /system/framework/telephony-common.jar (/data/dalvik-cache/system@framework@telephony-common.jar@classes.dex) 29 D/dalvikvm( 532): Unable to process classpath element '/system/framework/telephony-common.jar' 30 E/dalvikvm( 532): Could not stat dex cache directory '/data/dalvik-cache': No such file or directory 31 I/dalvikvm( 532): Unable to open or create cache for /system/framework/voip-common.jar (/data/dalvik-cache/system@framework@voip-common.jar@classes.dex) 32 D/dalvikvm( 532): Unable to process classpath element '/system/framework/voip-common.jar' 33 E/dalvikvm( 532): Could not stat dex cache directory '/data/dalvik-cache': No such file or directory 34 I/dalvikvm( 532): Unable to open or create cache for /system/framework/mms-common.jar (/data/dalvik-cache/system@framework@mms-common.jar@classes.dex) 35 D/dalvikvm( 532): Unable to process classpath element '/system/framework/mms-common.jar' 36 E/dalvikvm( 532): Could not stat dex cache directory '/data/dalvik-cache': No such file or directory 37 I/dalvikvm( 532): Unable to open or create cache for /system/framework/android.policy.jar (/data/dalvik-cache/system@framework@android.policy.jar@classes.dex) 38 D/dalvikvm( 532): Unable to process classpath element '/system/framework/android.policy.jar' 39 E/dalvikvm( 532): Could not stat dex cache directory '/data/dalvik-cache': No such file or directory 40 I/dalvikvm( 532): Unable to open or create cache for /system/framework/services.jar (/data/dalvik-cache/system@framework@services.jar@classes.dex) 41 D/dalvikvm( 532): Unable to process classpath element '/system/framework/services.jar' 42 E/dalvikvm( 532): Could not stat dex cache directory '/data/dalvik-cache': No such file or directory 43 I/dalvikvm( 532): Unable to open or create cache for /system/framework/apache-xml.jar (/data/dalvik-cache/system@framework@apache-xml.jar@classes.dex) 44 D/dalvikvm( 532): Unable to process classpath element '/system/framework/apache-xml.jar' 45 E/dalvikvm( 532): Could not stat dex cache directory '/data/dalvik-cache': No such file or directory 46 I/dalvikvm( 532): Unable to open or create cache for /system/framework/webviewchromium.jar (/data/dalvik-cache/system@framework@webviewchromium.jar@classes.dex) 47 D/dalvikvm( 532): Unable to process classpath element '/system/framework/webviewchromium.jar' 48 E/dalvikvm( 532): Could not stat dex cache directory '/data/dalvik-cache': No such file or directory 49 I/dalvikvm( 532): Unable to open or create cache for /system/framework/telephony-msim.jar (/data/dalvik-cache/system@framework@telephony-msim.jar@classes.dex) 50 D/dalvikvm( 532): Unable to process classpath element '/system/framework/telephony-msim.jar' 51 E/dalvikvm( 532): No valid entries found in bootclasspath 52 '/system/framework/core.jar:/system/framework/conscrypt.jar:/system/framework/okhttp.jar:/system/framework/core-junit.jar:/system/framework/bouncycastle.jar:/system/framework/ext.jar:/system/framework/framework.jar:/system/framework/framework2.jar:/system/framework/telephony-common.jar:/system/framework/voip-common.jar:/system/framework/mms-common.jar:/system/framework/android.policy.jar:/system/framework/services.jar:/system/framework/apache-xml.jar:/system/framework/webviewchromium.jar:/system/framework/telephony-msim.jar' 53 E/dalvikvm( 532): VM aborting 54 F/libc ( 532): Fatal signal 6 (SIGABRT) at 0x00000214 (code=-6), thread 532 (zygote) 55 I/ServiceManager( 180): service 'media.audio_flinger' died 56 I/ServiceManager( 180): service 'media.player' died 57 I/ServiceManager( 180): service 'media.camera' died
这理应是数据没有清除完成导致的，于是 Google下，尝试使用 fastboot -w 来清除数据，最后成功开机！
小结，Nexus 7 此类问题解决方法(黄背景的是重点，前两步可选)：
adb sideload /media/Source/CyanogenMod/out/cm-11.0/target/product/flo/cm-11-20141224-UNOFFICIAL-flo.zip
fastboot flash boot /media/Source/CyanogenMod/out/cm-11.0/target/product/flo/boot.img
fastboot -w