Introduction to HarmonyOS Next Logging Tools

In HarmonyOS Next development, logs are the primary means for debugging and problem-solving. Whether using hilog or console, logs can ultimately be output to the log module of DevEco Studio:

Here, you can filter by app process, log level, and content, and perform convenient searches. However, in scenarios with frequent log updates, we may want to output logs to files. While Android provides the logcat command to export logs to the console or files, HarmonyOS Next offers a similar tool: hilog.

Introduction to hilog Tool

The HiLog logging system is provided for system frameworks, services, and applications to print logs, record user operations, system status, etc. Developers can query log information via the hilog command line.

After installing DevEco Studio IDE or the HarmonyOS SDK and configuring the hdc command tool in the environment variables, you can use hdc to enter the device shell:

hdc shell

Once in the shell, execute hilog commands:

If logs refresh too quickly (less efficient than DevEco Studio's log tool), use hilog with parameters.

hilog Command Parameters

Short Option	Long Option	Parameter	Description
-h	--help		Help command.
Default	Default		Blocking log reading (does not exit).
-x	--exit		Non-blocking log reading (exits after reading).
-g			Query buffer size (use with -t to specify a type; defaults to app and core).
-G	--buffer-size		Set the buffer size for the specified (use with -t; defaults to app and core; units: B/K/M; range: 64K-16M).
-r			Clear buffer logs (use with -t; defaults to app and core).
-k			Kernel log reading control.
		on	Enable kernel log reading.
		off	Disable kernel log reading.
-s	--statistics		Query statistics (requires -t or -D).
-S			Clear statistics (requires -t or -D).
-Q			Flow control quota switch.
		pidon	Enable process flow control.
		pidoff	Disable process flow control.
		domainon	Enable domain flow control.
		domainoff	Disable domain flow control.
-L	--level		Specify log levels (e.g., -L D/I/W/E/F).
-t	--type		Specify log types (e.g., -t app/core/init/only_prerelease; app: app logs, core: system logs, init: boot logs, only_prerelease: logs for pre-release systems, irrelevant to app developers).
-D	--domain		Specify a domain.
-T	--tag		Specify a tag.
-a	--head		Display only the first lines of logs.
-z	--tail		Display only the last lines of logs.
-P	--pid		Identify different PIDs.
-e	--regex		Print only lines matching the regular expression .
-f	--filename		Set the disk file name.
-l	--length		Set the disk file size (must be ≥64K).
-n	--number		Set the number of disk files.
-j	--jobid		Set the disk task ID.
-w	--write		Disk task control.
		query	Query disk tasks.
		start	Start a disk task (command line parameters: filename, single file size, disk algorithm, number of rotate files).
		stop	Stop the disk task.
		refresh	Refresh buffer logs to disk files.
		clear	Delete existing disk log files.
-m	--stream		Disk storage algorithm control.
		none	Disk storage without compression.
		zlib	Disk storage with zlib compression (file extension: .gz).
		zstd	Disk storage with zstd compression (file extension: .zst).
-v	--format
		time	Display local time.
		color	Display different levels in different colors (default: black and white).
		epoch	Display time relative to 1970.
		monotonic	Display time relative to boot.
		usec	Display time with microsecond precision.
		nsec	Display time with nanosecond precision.
		year	Add the year to the displayed time.
		zone	Add the local time zone to the displayed time.
		wrap	When logs wrap, new lines do not add prefixes like timestamps.
-b	--baselevel		Set the minimum log level (D(DEBUG)/I(INFO)/W(WARN)/E(ERROR)/F(FATAL)).

Parameter Configuration Practices

Clear Buffer Logs

Logs are typically cached. To avoid interference from previous logs when starting an app, clear the cache:

$ hilog -r
Log type core,app,only_prerelease buffer clear successfully

Kernel Log Reading Control

Kernel logs are usually unnecessary during app debugging. Use hilog -k on/off to enable/disable them:

$ hilog -k on
Set hilogd storing kmsg log on successfully
$ 
$ hilog -k off
Set hilogd storing kmsg log off successfully

View Specified Level Logs

hilog -L D/I/W/E/F

View Specified Type Logs

hilog -t app

View Specified Domain Logs

hilog -D 01B06

View Specified TAG Logs

hilog -T tag

View Specified Process Logs

hilog -P pid

View Logs Matching Regex Keywords

hilog -e start

View and Set Disk Tasks

hilog -w control

• Query current tasks: hilog -w query
• Start hilog disk task with 1000 files: hilog -w start -n 1000
• Start kmsglog disk task with 100 files: hilog -w start -n 100 -t kmsg
• Stop current disk task: hilog -w stop
• Start kmsglog disk task with settings (compression: zlib/zstd/none): hilog -w start -t kmsg -f kmsglog -l 2M -n 100 -m zlib

Examples:

$ hilog -w query
Persist task query failed
No running persistent task [CODE: -63]
$
$ hilog -w start -n 1000
Persist task [jobid:1][fileNum:1000][fileSize:4194304] start successfully
$
$ hilog -w start -n 100 -t kmsg
Persist task [jobid:2][fileNum:100][fileSize:4194304] start successfully
$
$ hilog -w stop
Persist task [jobid:1] stop successfully
Persist task [jobid:2] stop successfully
$
$ hilog -w start -t kmsg -f kmsglog -l 2M -n 100 -m zlib
Persist task [jobid:2][fileNum:100][fileSize:2097152] start successfully

Set Log Display Format

hilog -v time/color/epoch/monotonic/usec/nsec/year/zone/wrap

This format setting facilitates console log viewing.

Set Minimum Printable Log Level

hilog -b D/I/W/E/F

If logs are not displayed, this setting may be the cause.

Introduction to hilogtool

Hilog logs are stored as encoded binary gz files. After exporting from the device's /data/log/hilog path, they cannot be directly unzipped and require parsing with the hilogtool to convert to plaintext:

The hilogtool is located in the SDK's hms/toolchains directory and used as follows:

• hilogtool parse -i xxx -o xxx -d xxx
• hilogtool parse –-input xxx –-output xxx --dict xxx

hilogtool Parsing Command Parameters

Option	Description	Example
-i/–-input inputDir	Specify the input path (scans all hilog files in the directory for parsing); defaults to the current directory.	Parse all hilog files in D:\temp\hilog: hilogtool parse -i D:\temp\hilog Parse current directory: hilogtool parse -i .
-i/–-input inputFile	Parse a single hilog file.	Parse a specific file: hilogtool parse -i D:\temp\data\log\hilog.706.20230711-071816.gz hilogtool parse -i .\hilog.706.20230711-071816.gz
-o/–-output outputDir	Specify the output path for parsed logs; defaults to the input file's directory.	Parse current directory logs to D:\temp: hilogtool parse -i .\ -o D:\temp
-d/--dict dictFile	Specify the path to the data dictionary; defaults to matching the latest dictionary (format: hilog_dict.20230908-142200.zip) in the current directory.	Parse hilog files in D:\temp\hilog with the dictionary in the same directory: hilogtool parse -i D:\temp\hilog -d D:\temp\hilog\hilog_dict.20230908-142200.zip

The data dictionary (format: hilog_dict.2024xxxx-xxxxxx.zip) is automatically generated at device boot in /data/log/hilog. Missing the dictionary may cause parsing failures; restarting the device regenerates it.

Reference Links

• hilog
• hilogtool

Summary

Hilog and hilogtool help developers understand and debug applications by providing a way to view past events and errors. However, these tools are specific to Huawei's HarmonyOS platform and may not apply to other operating systems.

If developing for HarmonyOS and needing to record and analyze logs, understanding hilog and hilogtool is essential. For other platforms, seek analogous tools and methods for log management.