正常情况下，每一个Android应用启动后都会对应一个进程，当前越来越多应用会有多个进程，为了推送，为了内存，或者为了保活。如何查看应用进程呢。

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1.DOS下面cmd，然后打开adb shell，直接ps命令，显示当前手机所有进程，如图所示：

2.利用(ps|grep 条目名称)命令，过滤自己需要的进程，比如列出条目里含有tencent字符的进程（包名里面含有该字符），则输入ps|grep tencent，如图所示则，QQ包含的进程下面几个：

各列参数意义：

USER 进程当前用户；

PID Process ID，进程ID；

PPID Process Parent ID，进程的父进程ID；

VSIZE Virtual Size，进程的虚拟内存大小；

RSS Resident Set Size，实际驻留"在内存中"的内存大小；

WCHAN 休眠进程在内核中的地址；

PC Program Counter；

NAME 进程名；

3.还有比较重要的两个是进程的Importance等级以及adj值，关于这两个定义大家可以不必深究，但是要有一定的理解，这两个玩意是具体决定了系统在资源吃紧的情况下该杀掉哪些进程。通过cat /proc/进程id/oom_adj可以看到当前进程的adj指，比如输入cat /proc/32366/oom_adj

cat查看进程的adj值后我们会得到其返回结果“0”，说明当前进程正位于前台，因为我的手机qq是打开的。
同样，我按home键，把qq退到后台，这个时候，再输入cat /proc/32366/oom_adj，则如下结果

而adj值则在ProcessList中定义：

final class ProcessList {
// OOM adjustments for processes in various states:

// Adjustment used in certain places where we don't know it yet.
// (Generally this is something that is going to be cached, but we
// don't know the exact value in the cached range to assign yet.)
static final int UNKNOWN_ADJ = 16;

// This is a process only hosting activities that are not visible,
// so it can be killed without any disruption.
static final int CACHED_APP_MAX_ADJ = 15;
static final int CACHED_APP_MIN_ADJ = 9;

// The B list of SERVICE_ADJ -- these are the old and decrepit
// services that aren't as shiny and interesting as the ones in the A list.
static final int SERVICE_B_ADJ = 8;

// This is the process of the previous application that the user was in.
// This process is kept above other things, because it is very common to
// switch back to the previous app.  This is important both for recent
// task switch (toggling between the two top recent apps) as well as normal
// UI flow such as clicking on a URI in the e-mail app to view in the browser,
// and then pressing back to return to e-mail.
static final int PREVIOUS_APP_ADJ = 7;

// This is a process holding the home application -- we want to try
// avoiding killing it, even if it would normally be in the background,
// because the user interacts with it so much.
static final int HOME_APP_ADJ = 6;

// This is a process holding an application service -- killing it will not
// have much of an impact as far as the user is concerned.
static final int SERVICE_ADJ = 5;

// This is a process with a heavy-weight application.  It is in the
// background, but we want to try to avoid killing it.  Value set in
// system/rootdir/init.rc on startup.
static final int HEAVY_WEIGHT_APP_ADJ = 4;

// This is a process currently hosting a backup operation.  Killing it
// is not entirely fatal but is generally a bad idea.
static final int BACKUP_APP_ADJ = 3;

// This is a process only hosting components that are perceptible to the
// user, and we really want to avoid killing them, but they are not
// immediately visible. An example is background music playback.
static final int PERCEPTIBLE_APP_ADJ = 2;

// This is a process only hosting activities that are visible to the
// user, so we'd prefer they don't disappear.
static final int VISIBLE_APP_ADJ = 1;

// This is the process running the current foreground app.  We'd really
// rather not kill it!
static final int FOREGROUND_APP_ADJ = 0;

// This is a process that the system or a persistent process has bound to,
// and indicated it is important.
static final int PERSISTENT_SERVICE_ADJ = -11;

// This is a system persistent process, such as telephony.  Definitely
// don't want to kill it, but doing so is not completely fatal.
static final int PERSISTENT_PROC_ADJ = -12;

// The system process runs at the default adjustment.
static final int SYSTEM_ADJ = -16;

// Special code for native processes that are not being managed by the system (so
// don't have an oom adj assigned by the system).
static final int NATIVE_ADJ = -17;
}

相较于Importance等级而言adj值可以赋予我们更多的参考价值，从上述adj值的定义中我们可以看到，值越小优先级越高，比如native进程的adj值为－17，对于这个adj值的进程来说，系统根本不会动它一分一毫，实质上当进程的adj值去到2时系统就很少会因为其它原因而去杀死它，这些在研究进程保活中都非常重要。

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如有错误欢迎指出来，一起学习。