Which service is doing what?

edit

In another question I was concerned about the iSCSI service taking precious boot time away, while I did not need this service at all.

I have also found that to improve boot time I could use systemd and systemctl:

• systemd-analyze blame
  returns a list of various services launched at boot and the time it took to launch them and do their thing in milliseconds.
• systemd-analyze plot > plot.svg
  creates a graphic plot of the latest boot in SVG format.
• systemctl stop SERVICENAME.service and systemctl disable SERVICENAME.service
  stop a running service and disable it at boot respectively.

etc. more on this post.

Now I removed some services based on the suggestion of more experienced and knowledgeable users. My boot dramatically was shortened by almost 60 % (from 62s to 26s!). Some of the services I removed were:

• sendmail.service
• sm-client.service
• iscsi.service
• udev-settle.service
• fedora-wait-storage.service

It is also suggested I should remove:

• fcoe.service

It seems that much services are running while I do not need them. On the other hand I have hardly any information about those services. Some are obvious in their use like the sendmail.service, others are more obscure like the fedora-wait-storage.service.

If I now run systemd-analyze blame it returns a list of services launched at boot. How can I find out what service does what? Is there a way to query these services about their identity and activity? Is there documentation? How to determine what service I need and which one I don't?

11885ms fedora-storage-init.service
  4966ms fedora-loadmodules.service
  3499ms systemd-vconsole-setup.service
  2744ms fedora-readonly.service
  2574ms remount-rootfs.service
  2436ms media.mount
  2416ms sys-kernel-debug.mount
  2405ms dev-hugepages.mount
  2397ms sys-kernel-security.mount
  2387ms dev-mqueue.mount
  1934ms udev-trigger.service
  1807ms netfs.service
  1679ms mdmonitor-takeover.service
  1622ms fcoe.service
  1608ms udev.service
  1493ms systemd-remount-api-vfs.service
   784ms sys-kernel-config.mount
   503ms fedora-storage-init-late.service
   492ms NetworkManager.service
   490ms systemd-sysctl.service
   410ms lvm2-monitor.service
   389ms avahi-daemon.service
   337ms console-kit-log-system-start.service
   291ms rsyslog.service
   256ms systemd-logind.service
   239ms livesys.service
   233ms ip6tables.service
   230ms iptables.service
   216ms systemd-readahead-replay.service
   213ms auditd.service
   211ms boot.mount
   207ms systemd-readahead-collect.service
   199ms sshd-keygen.service
   176ms irqbalance.service
   147ms abrt-vmcore.service
   146ms systemd-tmpfiles-setup.service
   134ms mcelog.service
   122ms abrt-ccpp.service
   114ms dbus.service
    79ms console-kit-daemon.service
    60ms sandbox.service
    37ms home.mount
    30ms livesys-late.service
    12ms systemd-user-sessions.service
     7ms rtkit-daemon.service
     7ms accounts-daemon.service
     0ms sys-fs-fuse-connections.mount