There might be ps utilities out there, that assume 80chars instead

of unlimited width if they cannot detect terminal size, therefore
force unlimited terminal size when checking processes via ps.

app/controllers/admin/background_jobs_controller.rb

@@ -1,6 +1,6 @@
 class Admin::BackgroundJobsController < Admin::ApplicationController
   def show
-    ps_output, _ = Gitlab::Popen.popen(%W(ps -U #{Gitlab.config.gitlab.user} -o pid,pcpu,pmem,stat,start,command))
+    ps_output, _ = Gitlab::Popen.popen(%W(ps ww -U #{Gitlab.config.gitlab.user} -o pid,pcpu,pmem,stat,start,command))
     @sidekiq_processes = ps_output.split("\n").grep(/sidekiq/)
     @concurrency = Sidekiq.options[:concurrency]
   end

changelogs/unreleased/fix_rake_gitlab_check_sidekiq.yml

@@ -0,0 +1,4 @@
+---
+title: Force unlimited terminal size when checking processes via call to ps
+merge_request: 10246
+author: Sebastian Reitenbach

lib/tasks/gitlab/check.rake

@@ -617,7 +617,7 @@ namespace :gitlab do
     end
 
     def sidekiq_process_count
-      ps_ux, _ = Gitlab::Popen.popen(%w(ps ux))
+      ps_ux, _ = Gitlab::Popen.popen(%w(ps uxww))
       ps_ux.scan(/sidekiq \d+\.\d+\.\d+/).count
     end
   end
@@ -751,7 +751,7 @@ namespace :gitlab do
     end
 
     def mail_room_running?
-      ps_ux, _ = Gitlab::Popen.popen(%w(ps ux))
+      ps_ux, _ = Gitlab::Popen.popen(%w(ps uxww))
       ps_ux.include?("mail_room")
     end
   end