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

app/controllers/admin/background_jobs_controller.rb

 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

+---
+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