SLF4J: Class path contains multiple SLF4J bindings. - Carbonio General

RE: SLF4J: Class path contains multiple SLF4J bindings.

LewisMiles — Wed, 13 May 2026 18:32:09 +0000

This warning means your classpath has more than one SLF4J binding (like slf4j-simple, slf4j-log4j12, or logback-classic) at the same time. SLF4J will still run, but it picks only one binding arbitrarily, which can lead to unexpected logging behavior.

To resolve it:

Look at the warning message to see which JARs are listed as bindings.
Run mvn dependency:tree (Maven) or ./gradlew dependencies (Gradle) to spot which dependencies pull in the extra SLF4J bindings.
Exclude the unwanted binding(s) from those dependencies in your pom.xml or build.gradle (for example, exclude slf4j-log4j12 if you’re using Logback).
Make sure your project depends on slf4j-api and keeps exactly one binding to removed link " target="_blank" rel="noopener">p avoid including multiple bindings in libraries or shared modules.

RE: SLF4J: Class path contains multiple SLF4J bindings.

LewisMiles — Wed, 13 May 2026 17:34:39 +0000

To resolve it:

Look at the warning message to see which JARs are listed as bindings.
Run mvn dependency:tree (Maven) or ./gradlew dependencies (Gradle) to spot which dependencies pull in the extra SLF4J bindings.
Exclude the unwanted binding(s) from those dependencies in your pom.xml or build.gradle (for example, exclude slf4jremoved link " target="_blank" rel="noopener">-log4j12 if you’re using Logback).
Make sure your project depends on slf4j-api and keeps exactly one binding: avoid including multiple bindings in libraries or shared modules.

RE: SLF4J: Class path contains multiple SLF4J bindings.

Sharif — Tue, 12 May 2026 07:47:30 +0000

@gailhamilton @lewismiles

You are right that the warning is harmless and trimming to a single binding is the cleanest direction. I'm afraid the trim does not quite stick as both binding copies are shipped by packages, so a manual rename would likely to be undone on the next upgrade.

RE: SLF4J: Class path contains multiple SLF4J bindings.

LewisMiles — Thu, 07 May 2026 10:00:47 +0000

This SLF4J warning occurs when multiple bindings (like slf4j-log4j12, logback-classic, log4j-slf4j-impl) compete on the classpath. SLF4J picks the first binding found (check console for "Actual binding is of type"), but others generate warning...

RE: SLF4J: Class path contains multiple SLF4J bindings.

gailhamilton — Sat, 25 Apr 2026 10:15:25 +0000

Though they are only warnings and not errors, they show a congested classpath where several logging bindings are contending. The simple solution is to keep only one binding and remove the other jars that are causing duplication, especially those packaged in different directories...

RE: SLF4J: Class path contains multiple SLF4J bindings.

gailhamilton — Wed, 22 Apr 2026 10:52:50 +0000

Messages indicate a cluttered classpath where several logging bindings are competing, but they are merely warnings and not errors. Keeping just one binding and eliminating the additional jars that are creating duplication—especially those wrapped in various directories—is the straightforward answer.

RE: SLF4J: Class path contains multiple SLF4J bindings.

gailhamilton — Wed, 22 Apr 2026 10:48:03 +0000

In Carbonio 24.7 before the last Carbonio upgrade to 24.9, there were 115 jar files in /opt/zextras/lib/jars folder including log4j-slf4j-impl-2.20.0.jar file. After upgrade, they are moved to new folder /opt/zextras/mailbox/jars along with many more total 170 jar files. Then there is a new carbonio-message-dispatcher-auth.jar in old lib/jars folder. Both folders are included in classpath within zmjava file. This new jar file also contains removed link thus causing the warning.

I guess Carbonio didn't set the class dependency correctly removed link " target="_blank" rel="noopener">TV Garden when they built the jar file and they have to issue a new update to fix it. I suspect there would be more of such duplicate.

Warning is just warning and it won't harm the operation except it is irritating to see them. I removed (renamed) log4j-slf4j-impl-2.20.0.jar file and calling zmprov and zmmailbox stopped giving the warning.

Yeah, you’re right—those SLF4J messages are just warnings, not errors, but they do point to a messy classpath where multiple logging bindings are competing. The clean fix is to keep only one binding (usually log4j-slf4j-impl or logback, not both) and remove the extra jars causing duplication, especially the ones bundled in different directories. It’s a bit like browsing something like “TV Garden”—if multiple streams of the same channel start playing at once, it still works, but the experience gets noisy and confusing, so trimming it down to a single source makes everything smoother and more predictable.

RE: SLF4J: Class path contains multiple SLF4J bindings.

djpark — Mon, 07 Oct 2024 16:03:32 +0000

I did this way (I do my maintenance as root).

# cd /opt/zextras/mailbox/jars
# mv log4j-slf4j-impl-2.20.0.jar log4j-slf4j-impl-2.20.0.jar..bak

Since the file permission & ownership are "-r--r--r-- root root", you will need to run as "sudo mv" instead of mv.

RE: SLF4J: Class path contains multiple SLF4J bindings.

arechick — Sun, 06 Oct 2024 03:13:15 +0000

hye djpark

I have facing the same problem with Nik. I just want to know how you rename the file since i have tried many time rename the file inside the /opt/zextras/mailbox/jars, its still coming out the warning and forbid the migration of my mailbox user. I also tried rename the file as .bak and suddenly all the migration were failed.now im clueless how to migrate my user mailbox into carbonio.

Please help.

RE: SLF4J: Class path contains multiple SLF4J bindings.

Nik — Thu, 03 Oct 2024 06:28:57 +0000

@djpark

Hi djpark,
good job, thanks a lot for your help.
Renaming the file you mentioned actually helped.
We will wait for the fix in the official release.

Good luck,
Nik