logcat

read-only

Streams the system log: the running commentary of everything happening on the phone.

Command: adb shell logcat
Commands: System and logs
Risk: read-only

Syntax

logcat [-v <format>]

Flags and arguments

Token	Meaning
-v <format>	Choose the line format. `threadtime` is the one worth having — date, time, pid, tid, level and tag; `brief` is the terser `I/Tag( 1234):` shape.

Examples

```
logcat -v threadtime
```
The format with every field, which is what a viewer should parse.
```
logcat -v brief
```
The older terse shape, still seen in pasted logs.

Reading the output

Sample output

07-26 13:37:01.234  1234  1250 I ActivityManager: Start proc 3062:com.example/u0a234
07-26 13:37:02.010  3062  3062 E MyApp   : java.lang.IllegalStateException: not attached

With `threadtime`: date, time, process id, thread id, one-letter level, tag, then the message after a colon and a space. The tag may contain spaces up to that colon. Not every line is a log record — `--------- beginning of main` and blank lines are the log's own banners, and a viewer should show them rather than try to parse them.

Output fields

Field	Meaning
MM-DD HH:MM:SS.mmm	The device's own local time. No time zone is printed.
pid tid	Process and thread id. Equal numbers mean the main thread.
V D I W E F	Verbose, Debug, Info, Warn, Error, Fatal — in increasing severity.
tag	Whatever the writer chose. The practical way to narrow a log down.
--------- beginning of …	A buffer boundary, not a record.

Version and vendor notes

This streams until something stops it, and on a busy phone that is thousands of lines a minute. Whatever consumes it needs a bound, or it grows until the machine complains.
A long line can be cut in half by the transport, so anything reading this must hold a partial line across chunk boundaries or it will corrupt roughly every hundredth line.
Which buffers exist, and which filter expressions this build understands, varies. Ask the device with `logcat --help` rather than assuming.

We have a UI for this

Android Logcat Viewer runs this command over USB and parses what comes back — a Chromium browser, no SDK, nothing uploaded.

Open Android Logcat Viewer

Related commands

Commands that turn up in the same session as logcat.

Command	What it does
dumpsys dropbox	The platform's ring buffer of crashes, ANRs and tombstones — how you read ANR traces without root.
dumpsys activity activities	Which app is in the foreground, and the task and stack structure behind it.
run-as	Runs a command as one app's own uid — the way to read a debug build's private files without root.

More System and logs commands

Command	What it does
top	A one-shot process table: CPU share, memory, state and command line.
getprop	Prints the system properties — the phone's own answer to what it is.

Checked against AOSP, toybox and kernel sources while writing the parsers behind our Web ADB tools. Where a behaviour genuinely varies by Android version or manufacturer, this page says so instead of giving a number that would be wrong on half the phones out there.

Frequently asked questions

How do I run an adb shell command?

Switch on developer options and USB debugging on the phone, plug it in, then run `adb shell <command>` from a machine with platform-tools installed — or run `adb shell` on its own to get an interactive prompt and type the command without the prefix. If the command produces binary output, such as a screenshot, use `adb exec-out` instead of `adb shell`: the plain shell service attaches a terminal, which rewrites newline bytes and corrupts the data.

Do adb shell commands need root?

Not the ones on this reference. They run as the `shell` user, which can manage packages for its own Android user, read most `dumpsys` services, write the settings provider, inject input and read shared storage. Root is only needed for things this reference deliberately avoids — reading another app's private data (except through `run-as` on a debuggable build), writing system partitions, or reading `/data/anr` directly.

Why does the output look different on my phone?

Either the Android version or the manufacturer. Some flags and fields arrived in a specific release, and those are noted per command. The rest is OEM patching, which hits `dumpsys` hardest: a dump is debug output whose text is whatever the service author last printed, and manufacturers change it and backport their changes. Read fields by name rather than by position, and treat an unfamiliar shape as a difference rather than as a failure.

Can I run this from a browser instead of a terminal?

For many commands, yes — the Web ADB tools on this site talk to a phone over WebUSB from a Chromium-based desktop browser, with no SDK installed and nothing uploaded. Each page links to the tool that runs its command, when one exists. Two limits are worth knowing: only one program can hold the ADB interface at a time, so a desktop `adb server` has to be stopped first, and `adb forward` and `adb reverse` cannot work in a browser at all.

Would rather click than type? The Web ADB Toolkit runs commands like this from a browser over USB. Or browse every command.