created_at2022-09-17 09:22:14.496809
updated_at2024-06-03 05:50:22.994837
descriptionSpeedily search and merge log messages by datetime. DateTime filters may be passed to narrow the search. s4 aims to be very fast.
James Thomas Moon (jtmoon79)



Super Speedy Syslog Searcher! (s4)

Speedily search and merge log messages by datetime.

MSRV License version downloads downloads (version) CHANGELOG

Build status Commits since

Super Speedy Syslog Searcher (s4) is a command-line tool to search and merge varying log messages from varying log files, sorted by datetime. Datetime filters may be passed to narrow the search to a datetime range.

s4 can read standardized log message formats like RFC 3164 and RFC 5424 ("syslog"), Red Hat Audit logs, strace output, and can read many non-standardized ad-hoc log message formats, including multi-line log messages. It also parses binary accounting records acct, lastlog, and utmp (acct, pacct, lastlog, utmp, utmpx, wtmp), systemd journal logs (.journal), and Microsoft Event Logs (.evtx). s4 can read logs that are compressed (.bz2, .gz, .lz4, .xz), or archived logs (.tar).

s4 aims to be very fast.


Install super_speedy_syslog_searcher

Assuming rust is installed, run

cargo install --locked super_speedy_syslog_searcher

Run s4

For example, print all the log messages in syslog files under /var/log/

s4 /var/log

On Windows, print the ad-hoc logs under C:\Windows\Logs

s4.exe C:\Windows\Logs

On Windows, print all .log files under C:\Windows (with the help of Powershell)

Get-ChildItem -Filter '*.log' -File -Path "C:\Windows" -Recurse -ErrorAction SilentlyContinue `
  | Select-Object -ExpandProperty FullName `
  | s4.exe -

(note that UTF-16 encoded logs cannot be parsed, see Issue #16)

(note that opening too many files causes error too many files open, see Issue #270, so Get-ChildItem -Filter lessens the number of files opened by s4.exe)

On Windows, print the Windows Event logs

s4.exe C:\Windows\System32\winevt\Logs

Print the log messages after January 1, 2022 at 00:00:00

s4 /var/log -a 20220101

Print the log messages from January 1, 2022 00:00:00 to January 2, 2022

s4 /var/log -a 20220101 -b 20220102


s4 /var/log -a 20220101 -b @+1d

Print the log messages on January 1, 2022, from 12:00:00 to 16:00:00

s4 /var/log -a 20220101T120000 -b 20220101T160000

Print the record-keeping log messages from up to a day ago (with the help of find)

find /var -xdev -type f \( \
    -name 'lastlog' \
    -or -name 'wtmp' \
    -or -name 'wtmpx' \
    -or -name 'utmp' \
    -or -name 'utmpx' \
    -or -name 'acct' \
    -or -name 'pacct' \
  \) \
    2>/dev/null \
    | s4 - -a=-1d

Print the journal log messages from up to an hour ago, prepending the journal file name (with the help of find)

find / -xdev -name '*.journal' -type f 2>/dev/null \
    | s4 - -a=-1h -n

Print only the log messages that occurred two days ago (with the help of GNU date)

s4 /var/log -a $(date -d "2 days ago" '+%Y%m%d') -b @+1d

Print only the log messages that occurred two days ago during the noon hour (with the help of GNU date)

s4 /var/log -a $(date -d "2 days ago 12" '+%Y%m%dT%H%M%S') -b @+1h

Print only the log messages that occurred two days ago during the noon hour in Bengaluru, India (timezone offset +05:30) and prepended with equivalent UTC datetime (with the help of GNU date)

s4 /var/log -u -a $(date -d "2 days ago 12" '+%Y%m%dT%H%M%S+05:30') -b @+1h


Speedily search and merge log messages by datetime.
DateTime filters may be passed to narrow the search.
s4 aims to be very fast.

Usage: s4 [OPTIONS] <PATHS>...

  <PATHS>...  Path(s) of log files or directories.
              Directories will be recursed. Symlinks will be followed.
              Paths may also be passed via STDIN, one per line. The user must
              supply argument "-" to signify PATHS are available from STDIN.

  -a, --dt-after <DT_AFTER>
          DateTime Filter After: print log messages with a datetime that is at
          or after this datetime. For example, "20200102T120000" or "-5d".
  -b, --dt-before <DT_BEFORE>
          DateTime Filter Before: print log messages with a datetime that is at
          or before this datetime.
          For example, "2020-01-03T23:00:00.321-05:30" or "@+1d+11h"
  -t, --tz-offset <TZ_OFFSET>
          Default timezone offset for datetimes without a timezone.
          For example, log message "[20200102T120000] Starting service" has a
          datetime substring "20200102T120000".
          That datetime substring does not have a timezone offset
          so this TZ_OFFSET value would be used.
          Example values, "+12", "-0800", "+02:00", or "EDT".
          To pass a value with leading "-" use "=" notation, e.g. "-t=-0800".
          If not passed then the local system timezone offset is used.
          [default: -07:00]
  -z, --prepend-tz <PREPEND_TZ>
          Prepend a DateTime in the timezone PREPEND_TZ for every line.
          Used in PREPEND_DT_FORMAT.
  -u, --prepend-utc
          Prepend a DateTime in the UTC timezone offset for every line.
          This is the same as "--prepend-tz Z".
          Used in PREPEND_DT_FORMAT.
  -l, --prepend-local
          Prepend DateTime in the local system timezone offset for every line.
          This is the same as "--prepend-tz +XX" where +XX is the local system
          timezone offset.
          Used in PREPEND_DT_FORMAT.
  -d, --prepend-dt-format <PREPEND_DT_FORMAT>
          Prepend a DateTime using the strftime format string.
          If PREPEND_TZ is set then that value is used for any timezone offsets,
          i.e. strftime "%z" "%:z" "%Z" values, otherwise the timezone offset value
          is the local system timezone offset.
          [Default: %Y%m%dT%H%M%S%.3f%z]
  -n, --prepend-filename
          Prepend file basename to every line.
  -p, --prepend-filepath
          Prepend file full path to every line.
  -w, --prepend-file-align
          Align column widths of prepended data.
      --prepend-separator <PREPEND_SEPARATOR>
          Separator string for prepended data.
          [default: :]
      --separator <LOG_MESSAGE_SEPARATOR>
          An extra separator string between printed log messages.
          Per log message not per line of text.
          Accepts a basic set of backslash escape sequences,
          e.g. "\0" for the null character, "\t" for tab, etc.
      --journal-output <JOURNAL_OUTPUT>
          The format for .journal file log messages.
          Matches journalctl --output options.
          [default: short]
          [possible values: short, short-precise, short-iso, short-iso-precise,
          short-full, short-monotonic, short-unix, verbose, export, cat]
  -c, --color <COLOR_CHOICE>
          Choose to print to terminal using colors.
          [default: auto]
          [possible values: always, auto, never]
      --blocksz <BLOCKSZ>
          Read blocks of this size in bytes.
          May pass value as any radix (hexadecimal, decimal, octal, binary).
          Using the default value is recommended.
          Most useful for developers.
          [default: 65535]
  -s, --summary
          Print a summary of files processed to stderr.
          Most useful for developers.
  -h, --help
          Print help
  -V, --version
          Print version

Given a file path, the file format will be processed based on a best guess of
the file name.
If the file format is not guessed then it will be treated as a UTF8 text file.
Given a directory path, found file names that have well-known non-log file name
extensions will be skipped.

DateTime Filters may be strftime specifier patterns:
    "%Y-%m-%d %H:%M:%S*"
    "%Y/%m/%d %H:%M:%S*"
Each * is an optional trailing 3-digit fractional sub-seconds,
or 6-digit fractional sub-seconds, and/or timezone.

Pattern "+%s" is Unix epoch timestamp in seconds with a preceding "+".
For example, value "+946684800" is be January 1, 2000 at 00:00, GMT.

DateTime Filters may be custom relative offset patterns:
    "+DwDdDhDmDs" or "-DwDdDhDmDs"
    "@+DwDdDhDmDs" or "@-DwDdDhDmDs"

Custom relative offset pattern "+DwDdDhDmDs" and "-DwDdDhDmDs" is the offset
from now (program start time) where "D" is a decimal number.
Each lowercase identifier is an offset duration:
"w" is weeks, "d" is days, "h" is hours, "m" is minutes, "s" is seconds.
For example, value "-1w22h" is one week and twenty-two hours in the past.
Value "+30s" is thirty seconds in the future.

Custom relative offset pattern "@+DwDdDhDmDs" and "@-DwDdDhDmDs" is relative
offset from the other datetime.
Arguments "-a 20220102 -b @+1d" are equivalent to "-a 20220102 -b 20220103".
Arguments "-a @-6h -b 20220101T120000" are equivalent to
"-a 20220101T060000 -b 20220101T120000".

Without a timezone, the Datetime Filter is presumed to be the local
system timezone.

Command-line passed timezones may be numeric timezone offsets,
e.g. "+09:00", "+0900", or "+09", or named timezone offsets, e.g. "JST".
Ambiguous named timezones will be rejected, e.g. "SST".

--prepend-tz and --dt-offset function independently:
--dt-offset is used to interpret processed log message datetime stamps that
do not have a timezone offset.
--prepend-tz affects what is pre-printed before each printed log message line.

--separator accepts backslash escape sequences:
    "\0", "\a", "\b", "\e", "\f", "\n", "\r", "\\", "\t", "\v"

Resolved values of "--dt-after" and "--dt-before" can be reviewed in
the "--summary" output.

DateTime strftime specifiers are described at

DateTimes supported are only of the Gregorian calendar.

DateTimes supported language is English.

Further background and examples are at the project website:

Is s4 failing to parse a log file? Report an Issue at


Why s4?

Super Speedy Syslog Searcher (s4) is meant to aid Engineers in reviewing varying log files in a datetime-sorted manner. The primary use-case is to aid investigating problems wherein the time of a problem occurrence is known and there are many available logs but otherwise there is little source evidence.

Currently, log file formats vary widely. Most logs are an ad-hoc format. Even separate log files on the same system for the same service may have different message formats! Sorting these logged messages by datetime may be prohibitively difficult. The result is an engineer may have to "hunt and peck" among many log files, looking for problem clues around some datetime; so tedious!

Enter Super Speedy Syslog Searcher 🦸 β€Ό

s4 will print log messages from multiple log files in datetime-sorted order. A "window" of datetimes may be passed, to constrain the period of printed messages. This will assist an engineer that, for example, needs to view all log messages that occurred two days ago between 12:00 and 12:05 among log files taken from multiple systems.

The ulterior motive for Super Speedy Syslog Searcher was the primary developer wanted an excuse to learn rust πŸ¦€, and wanted to create an open-source tool for a recurring need of some Software Test Engineers πŸ˜„

See the real-world example rationale in the section below, logging chaos: the problem s4 solves.


File name guessing

Given a file path, s4 will attempt to parse it. The type of file must be in the name. Guesses are made about files with non-standard names.

For example, standard file name utmp will always be treated as a utmp record file. But non-standard name log.utmp.1 is guessed to be a utmp record file. Similar guesses are applied to lastlog, wtmp, acct, pacct, journal, and evtx files. When combined with compression or archive file name extensions, e.g. .bz2, .gz, .lz4, or .xz, then s4 makes a best attempt at guessing the compression or archive type and the file within the archive based on the name. For example, user.journal.gz is guessed to be a systemd journal file within a gzip compressed file. However, if that same file is named something unusual like user.systemd-journal.gz then it is guessed to be a text log file within a gzip compressed file.

When a file type cannot be guessed then it is treated as a UTF8 text log file. For example, a file name just unknown is not any obvious type so it is attempted to be parsed as a UTF8 ad-hoc text log file.

tar files are inspected for parseable files.[2]

Directory walks

Given a directory path, s4 will walk the directory and all subdirectories and follow symbolic links and cross file system paths. s4 will ignore files with extensions that are known to be non-log files. For example, files with extensions .dll, .mp3, .png, or .so, are unlikely to be log files and so are not processed.

So given a file /tmp/file.mp3, an invocation of s4 /tmp will not attempt to process file.mp3. An invocation of s4 /tmp/file.mp3 will attempt to process file.mp3. It will be treated as a UTF8 text log file.


  • Only processes UTF-8 or ASCII encoded syslog files. (Issue #16)
  • Cannot process multi-file .gz files (only processes first stream found). (Issue #8)
  • Cannot process multi-file .xz files (only processes first stream found). (Issue #11)
  • Cannot process .zip archives (Issue #39)
  • [1] ISO 8601
    • ISO 8601 forms recognized (using ISO descriptive format)
      • YYYY-MM-DDThh:mm:ss
      • YYYY-MM-DDThhmmss
      • YYYYMMDDThhmmss (may use date-time separator character 'T' or character blank space ' ')
    • ISO 8601 forms not recognized:
  • [2] Cannot process archive files or compressed files within other archive files or compressed files (Issue #14)
    e.g. cannot process logs.tar.xz, nor file log.gz within logs.tar




An overview of features of varying log mergers including GNU tools.

βœ” Yes
⬀ Most
β—’ Some
βœ— No
☐ with an accompanying GNU program
! with user input
β€Ό with complex user input

General Features

Program Source CLI TUI Interactive live tail merge varying log formats datetime search range
grep | sort C βœ” βœ— βœ— ☐ tail βœ— β€Ό
s4 Rust βœ” βœ— βœ— βœ— βœ” βœ”
logmerger Python βœ” βœ” βœ” βœ— β€Ό βœ”
tl Python βœ” βœ” βœ” βœ” βœ— βœ— Python βœ” βœ— βœ— βœ— βœ— βœ—

Formal Log DateTime Supported

Program RFC 2822 RFC 3164 RFC 3339 RFC 5424 ISO 8601
grep | sort βœ— β€Ό ! ! !
s4 βœ” βœ” βœ” βœ” βœ”
logmerger βœ— βœ— ! ! β—’
tl βœ— βœ— βœ” βœ” βœ”

Other Log or File Formats Supported

Program Ad-hoc text formats Red Hat Audit Log journal acct/lastlog/utmp .evtx .pcap/.pcapng .jsonl strace
grep | sort β€Ό ! βœ— βœ— βœ— βœ— βœ— βœ”
s4 βœ” βœ” βœ” βœ” βœ” βœ— βœ” βœ”
logmerger β€Ό β€Ό βœ— βœ— βœ— βœ” βœ— βœ”
tl βœ— βœ— βœ— βœ— βœ— βœ— βœ” βœ—

Archive Formats Supported

Program .gz .lz4 .bz .bz2 .xz .tar .zip
grep | sort ☐ zgrep ☐ lz4 ☐ bzip ☐ bzip2 ☐ xz βœ— βœ—
s4 βœ” βœ” βœ— βœ” βœ” βœ” βœ—
logmerger βœ” βœ— βœ— βœ— βœ— βœ— βœ—
tl βœ” βœ— βœ” βœ” βœ— βœ— βœ— βœ” βœ— βœ— βœ— βœ— βœ— βœ—

Speed Comparison

A comparison of merging three large log files:

  • 2000 line log file, 1116357 bytes (β‰ˆ1.1 MB), with high-plane unicode
  • 2500 line log file, 1078842 bytes (β‰ˆ1.0 MB), with high-plane unicode
  • 5000 line log file, 2158138 bytes (β‰ˆ2.1 MB), with high-plane unicode
Program real user sys
grep | sort 0.04 0.03 0.00
s4 0.05 0.06 0.01
logmerger 0.72 0.69 0.02
tl 1.30 0.47 0.06

This informal runtime comparison used GNU time running on Ubuntu 22 on WSL2.

  • grep 3.7, sort 8.32
  • s4 0.7.73
  • logmerger 0.9.0 on Python 3.10.12
  • tl 1.5.0 on Python 3.10.12

See directory compare-log-mergers and results in compare-log-mergers.txt.

Building locally

Building on Linux requires:

  • rust minimal or more
  • gcc (which should install cc, libc, and libc-headers)

Building on Windows requires Visual Studio. rustup-init.exe will help install the necessary tools.

From the git cloned project directory run cargo build.

Parsing .journal files

Requires libsystemd to be installed to use at runtime.

Requesting Support For DateTime Formats; your particular log file

If you have found a log file that Super Speedy Syslog Searcher does not parse then you may create a new Issue type Feature request (datetime format).

Here is an example user-submitted Issue.

"syslog" and other project definitions


In this project, the term "syslog" is used generously to refer to any log message that has a datetime stamp on the first line of log text.

Technically, "syslog" is defined among several RFCs proscribing fields, formats, lengths, and other technical constraints. In this project, the term "syslog" is interchanged with "log".

The term "sysline" refers to a one log message which may comprise multiple text lines.

See docs section Definitions of data for more project definitions.

log message

A "log message" is a single log entry for any type of logging scheme; an entry in a utmpx file, an entry in a systemd journal, an entry in a Windows Event Log, a formal RFC 5424 syslog message, or an ad-hoc log message.

logging chaos: the problem s4 solves

In practice, most log file formats are an ad-hoc format. And among formally defined log formats, there are many variations. The result is merging varying log messages by datetime is prohibitively tedious. If an engineer is investigating a problem that is symptomatic among many log files then the engineer must "hunt and peck" among those many log files. Log files can not be merged for a single coherent view.

The following real-world example log files are available in project directory ./logs.

open-source software examples

nginx webserver

For example, the open-source nginx web server logs access attempts in an ad-hoc format in the file access.log - - [08/Oct/2022:22:26:35 +0000] "GET /DOES-NOT-EXIST HTTP/1.1" 404 0 "-" "curl/7.76.1" "-"

which is an entirely dissimilar log format to the neighboring nginx log file, error.log

2022/10/08 22:26:35 [error] 6068#6068: *3 open() "/usr/share/nginx/html/DOES-NOT-EXIST" failed (2: No such file or directory), client:, server: _, request: "GET /DOES-NOT-EXIST HTTP/1.0", host: ""

nginx is following the bad example set by the apache web server.

Debian 11

Here are log snippets from a Debian 11 host.

file /var/log/alternatives.log

update-alternatives 2022-10-10 23:59:47: run with --quiet --remove rcp /usr/bin/ssh

file /var/log/dpkg.log

2022-10-10 15:15:02 upgrade gpgv:amd64 2.2.27-2 2.2.27-2+deb11u1

file /var/log/kern.log

Oct 10 23:07:16 debian11-b kernel: [    0.10034] Linux version 5.10.0-11-amd64

file /var/log/unattended-upgrades/unattended-upgrades-shutdown.log

2022-10-10 23:07:16,775 WARNING - Unable to monitor PrepareForShutdown() signal, polling instead.

binary files

And then there are binary files, such as the wtmp file on Linux and other Unix Operating Systems. Using tool utmpdump, a utmp record structure is converted to text like:

[7] [12103] [ts/0] [user] [pts/0] [] [] [2023-03-05T23:12:36,270185+00:00]

And from a systemd .journal file, read using journalctl

Mar 03 10:26:10 host systemd[1]: Started OpenBSD Secure Shell server.
β–‘β–‘ Subject: A start job for unit ssh.service has finished successfully
β–‘β–‘ Defined-By: systemd
β–‘β–‘ Support:
β–‘β–‘ A start job for unit ssh.service has finished successfully.
β–‘β–‘ The job identifier is 120.
Mar 03 10:31:23 host sshd[4559]: Accepted login for user1 from port 51730 ssh2

Try merging those two log messages by datetime using GNU grep, sort, sed, or awk!

Additionally, if the wtmp file is from a different architecture or Operating System, then the binary record structure is likely not parseable by the resident utmpdump tool. What then!?

commercial software examples

Commercial software and computer hardware vendors nearly always use ad-hoc log message formatting that is even more unpredictable among each log file on the same system.

Synology DiskStation

Here are log file snippets from a Synology DiskStation host.

file DownloadStation.log

2019/06/23 21:13:34	(system) trigger DownloadStation 3.8.13-3519 Begin start-stop-status start

file sfdisk.log

2019-04-06T01:07:40-07:00 dsnet sfdisk: Device /dev/sdq change partition.

file synobackup.log

info	2018/02/24 02:30:04	SYSTEM:	[Local][Backup Task Backup1] Backup task started.

(yes, those are tab characters)

Mac OS 12

Here are log file snippets from a Mac OS 12.6 host.

file /var/log/system

Sep 22 00:01:21 Mac-mini syslogd[108]: ASL Sender Statistics
Sep 22 00:06:22 Mac-mini halt[78568]: SHUTDOWN_TIME: 1695341182 412865
Oct 11 15:04:44 localhost bootlog[0]: BOOT_TIME 1697036684 0
Oct 11 15:04:55 localhost syslogd[110]: Configuration Notice:
	ASL Module "" claims selected messages.
	Those messages may not appear in standard system log files or in the ASL database.

file /var/log/wifi

Thu Sep 21 23:05:35.850 Usb Host Notification NOT activated
Fri Sep 22 15:05:01.994 Usb Host Notification activated!

file /var/log/fsck_hs.log

/dev/rdisk2s2: fsck_hfs started at Thu Sep 21 21:31:05 2023
/dev/rdisk2s2: /dev/rdisk2s2: ** /dev/rdisk2s2 (NO WRITE)
/dev/rdisk2s2:    Executing fsck_hfs (version hfs-583.100.10).
/dev/rdisk2s2: fsck_hfs completed at Thu Sep 21 21:31:05 2023

file /var/log/anka.log

Fri Sep 22 00:06:05 UTC 2023: Checking /Library/Developer/CoreSimulator/Volumes/watchOS_20S75...
Fri Sep 22 00:06:05 UTC 2023: No updates found

file /var/log/displaypolicyd.log

2023-09-15 04:26:56.329071-0700: Version: V6.5.7 starting [0]
2023-09-15 04:26:56.330256-0700: Started at Fri Sep 15 04:26:56 2023
2023-09-15 04:27:17.163031-0700: exit at user request Fri Sep 15 04:27:17 2023

file /var/log/

2023-10-26 16:56:23.171019 <Notice>: Doing boot task: restore-datapartition
2023-10-26 16:56:23.271137 <Notice>: Doing boot task: enable-swap
2023-10-26 16:56:23.287770 <Notice>: swap enabled

file /var/log/asl/logs/aslmanager.20231026T170200+00

Oct 26 17:02:00: aslmanager starting
Oct 26 17:02:00: Processing data store /var/log/asl
Oct 26 17:02:00: Data Store Size = 325176

Did you also notice how the log file names differ in unexpected ways?

Microsoft Windows 10

Here are log snippets from a Windows 10 host.

file ${env:SystemRoot}\debug\mrt.log

Microsoft Windows Malicious Software Removal Tool v5.83, (build 5.83.13532.1)
Started On Thu Sep 10 10:08:35 2020

file ${env:SystemRoot}\comsetup.log

COM+[12:24:34]: ********************************************************************************
COM+[12:24:34]: Setup started - [DATE:05,27,2020 TIME: 12:24 pm]
COM+[12:24:34]: ********************************************************************************

file ${env:SystemRoot}\DirectX.log

11/01/19 20:03:40: infinst: Installed file C:\WINDOWS\system32\xactengine2_1.dll

file ${env:SystemRoot}/Microsoft.NET/Framework/v4.0.30319/ngen.log

09/15/2022 14:13:22.951 [515]: 1>Warning: System.IO.FileNotFoundException: Could not load file or assembly

file ${env:SystemRoot}/Performance/WinSAT/winsat.log

68902359 (21103) - exe\logging.cpp:0841: --- START 2022\5\17 14:26:09 PM ---
68902359 (21103) - exe\main.cpp:4363: WinSAT registry node is created or present

(yes, it reads hour 14, and PM… πŸ™„)


This chaotic logging approach is typical of commercial and open-source software, AND IT'S A MESS! Attempting to merge log messages by their natural sort mechanism, a datetime stamp, is difficult to impossible.

Hence the need for Super Speedy Syslog Searcher! 🦸 s4 merges varying log files into a single coherent datetime-sorted log.

Further Reading


Stargazers over time

profile for @JamesThomasMoon on Stack Exchange, a network of free, community-driven Q&A sites
Commit count: 1856

cargo fmt