undefined method `have_capability?' for nil"

[Watson1978]

Discussed in #5151

^{Originally posted by krish0596 November 13, 2025}

What is a problem?

I am getting this error
2025-11-13 09:34:22 +0000 [error]: fluent/log.rb:414:error: unexpected error error_class=NoMethodError error="undefined method have_capability?' for nil"`
when trying to load a containerized fluentd image with added capablities through daemon set, not able to resolve this issue

Environment

• Linux / macOS
• Fluentd 1.19.0 / 1.19.1

How to reproduce

• configuration

<source>
  @type tail
  tag test

  # 1. Use file glob (*) to reproduce the error.
  # 2. Specify the path owned by other user.
  path /var/log/*.log

  <parse>
    @type none
  </parse>
</source>

<match **>
  @type stdout
</match>

• result

$ ruby bin/fluentd -c ~/prj/sandbox/fluentd/capability.conf
2025-11-21 14:05:32 +0900 [info]: init supervisor logger path=nil rotate_age=nil rotate_size=nil
2025-11-21 14:05:32 +0900 [info]: parsing config file is succeeded path="/home/watson/prj/sandbox/fluentd/capability.conf"
2025-11-21 14:05:32 +0900 [info]: inaccessible include directory was specified path="/etc/fluent/conf.d"
2025-11-21 14:05:32 +0900 [info]: gem 'fluent-plugin-parser-winevt_xml' version '0.2.8'
2025-11-21 14:05:32 +0900 [info]: gem 'fluent-plugin-splunk-enterprise' version '0.10.2'
2025-11-21 14:05:32 +0900 [info]: gem 'fluent-plugin-splunk-hec' version '1.3.3'
2025-11-21 14:05:32 +0900 [info]: gem 'fluentd' version '1.19.1'
2025-11-21 14:05:32 +0900 [error]: unexpected error error_class=NoMethodError error="undefined method 'have_capability?' for nil"

My machine has following files in /var/log

$ ls -l /var/log/*.log
-rw-r--r-- 1 root root  43997 11月 21 10:52 /var/log/Xorg.0.log
-rw-r--r-- 1 root root  47791  1月 22  2025 /var/log/Xorg.1.log
-rw-r--r-- 1 root root  49470 11月 17 18:39 /var/log/Xorg.2.log
-rw------- 1 root root  14867 11月 21 10:52 /var/log/boot.log
-rw-r--r-- 1 root root 886824 11月 21 10:32 /var/log/pacman.log

When permissions are set in a way that makes them inaccessible to other users, such as /var/log/boot.log, then, specifying to read a file using glob, it causes an error.

[Watson1978]

Hmm, @capability instance variable will be available at
https://github.com/fluent/fluentd/blob/08f8c24f849a3f7533ae2bee09f760360506d24b/lib/fluent/plugin/in_tail.rb#L198C1-L198C61

However, the instance variable has been used at

fluentd/lib/fluent/plugin/in_tail.rb

Line 168 in 08f8c24

check_dir_permission unless Fluent.windows?

before the instance variable is available.

• check_dir_permission -> expand_paths_raw -> have_read_capability? => causes undefined method 'have_capability?' for nil error

[Watson1978]

Related to #4865

[Watson1978]

@capability should be initialized earlier.

diff --git a/lib/fluent/plugin/in_tail.rb b/lib/fluent/plugin/in_tail.rb
index c037dc45..63ab326f 100644
--- a/lib/fluent/plugin/in_tail.rb
+++ b/lib/fluent/plugin/in_tail.rb
@@ -124,6 +124,7 @@ def initialize
     attr_reader :paths
 
     def configure(conf)
+      @capability = Fluent::Capability.new(:current_process)
       @variable_store = Fluent::VariableStore.fetch_or_build(:in_tail)
       compat_parameters_convert(conf, :parser)
       parser_config = conf.elements('parse').first
@@ -195,7 +196,6 @@ def configure(conf)
       @dir_perm = system_config.dir_permission || Fluent::DEFAULT_DIR_PERMISSION
       # parser is already created by parser helper
       @parser = parser_create(usage: parser_config['usage'] || @parser_configs.first.usage)
-      @capability = Fluent::Capability.new(:current_process)
       if @read_bytes_limit_per_second > 0
         if !@enable_watch_timer
           raise Fluent::ConfigError, "Need to enable watch timer when using log throttling feature"