针对系统管理员的文章：Systemd （一）验证启动

就像大家知道的那样，systemd是Fedora自Fedora14版以来的新的初始化系统，并且它也正在试图被一系列的其他Linux发行版所认可，就像OpenSUSE那样。对于系统管理员来说，systemd提供了一系列的新功能和改变，并大体上增强了管理的方法。在每一帖中我将尝试阐述systemd的一个新功能。它们中的许多短小而精悍，因此应该能提起一大批读者的兴趣。（呵呵）。但是，我们将引导你一点一点深入systemd为你提供的创新功能。

验证启动

从传统意义上说，当启动一个Linux系统时，你将看到许多信息飘过你的屏幕。在我们致力于加速启动并并行化启动进程的现在，这些信息出现的速度将会越来越快，并且越来越难以被阅读（因为你跟不上，而且我们还有图形化启动技术就像Plymouth）。尽管如此，启动屏幕的信息曾经是现在也是非常有用的，因为它显示了开机启动的服务是否成功的启动（通过那些绿色的[OK]和红色的[FAILED]）。为了改进启动的快速化和并行化，同时在运行期间更容易的被获得，我们在systemd中添加了一项功能，使能跟踪并记住每一项服务的状态：是否它成功启动，是否它以非0错误码退出，是否它超时，是否它不正常的被终止（段错误或类似的）。这项功能同时记录启动与运行这两个时刻。很简单地，使用systemctl命令就可以查询所有服务的状态，包括使用systemd的新式语法的服务和SysV/LSB的老式服务。

[root@lambda] ~# systemctl
UNIT                                          LOAD   ACTIVE       SUB          JOB             DESCRIPTION
dev-hugepages.automount                       loaded active       running                      Huge Pages File System Automount Point
dev-mqueue.automount                          loaded active       running                      POSIX Message Queue File System Automount Point
proc-sys-fs-binfmt_misc.automount             loaded active       waiting                      Arbitrary Executable File Formats File System Automount Point
sys-kernel-debug.automount                    loaded active       waiting                      Debug File System Automount Point
sys-kernel-security.automount                 loaded active       waiting                      Security File System Automount Point
sys-devices-pc...0000:02:00.0-net-eth0.device loaded active       plugged                      82573L Gigabit Ethernet Controller[...]sys-devices-virtual-tty-tty9.device           loaded active       plugged                      /sys/devices/virtual/tty/tty9
-.mount                                       loaded active       mounted                      /
boot.mount                                    loaded active       mounted                      /boot
dev-hugepages.mount                           loaded active       mounted                      Huge Pages File System
dev-mqueue.mount                              loaded active       mounted                      POSIX Message Queue File System
home.mount                                    loaded active       mounted                      /home
proc-sys-fs-binfmt_misc.mount                 loaded active       mounted                      Arbitrary Executable File Formats File System
abrtd.service                                 loaded active       running                      ABRT Automated Bug Reporting Tool
accounts-daemon.service                       loaded active       running                      Accounts Service
acpid.service                                 loaded active       running                      ACPI Event Daemon
atd.service                                   loaded active       running                      Execution Queue Daemon
auditd.service                                loaded active       running                      Security Auditing Service
avahi-daemon.service                          loaded active       running                      Avahi mDNS/DNS-SD Stack
bluetooth.service                             loaded active       running                      Bluetooth Manager
console-kit-daemon.service                    loaded active       running                      Console Manager
cpuspeed.service                              loaded active       exited                       LSB: processor frequency scaling support
crond.service                                 loaded active       running                      Command Scheduler
cups.service                                  loaded active       running                      CUPS Printing Service
dbus.service                                  loaded active       running                      D-Bus System Message Bus
getty@tty2.service                            loaded active       running                      Getty on tty2
getty@tty3.service                            loaded active       running                      Getty on tty3
getty@tty4.service                            loaded active       running                      Getty on tty4
getty@tty5.service                            loaded active       running                      Getty on tty5
getty@tty6.service                            loaded active       running                      Getty on tty6
haldaemon.service                             loaded active       running                      Hardware Manager
hdapsd@sda.service                            loaded active       running                      sda shock protection daemon
irqbalance.service                            loaded active       running                      LSB: start and stop irqbalance daemon
iscsi.service                                 loaded active       exited                       LSB: Starts and stops login and scanning of iSCSI devices.
iscsid.service                                loaded active       exited                       LSB: Starts and stops login iSCSI daemon.
livesys-late.service                          loaded active       exited                       LSB: Late init script for live image.
livesys.service                               loaded active       exited                       LSB: Init script for live image.
lvm2-monitor.service                          loaded active       exited                       LSB: Monitoring of LVM2 mirrors, snapshots etc. using dmeventd or progress polling
mdmonitor.service                             loaded active       running                      LSB: Start and stop the MD software RAID monitor
modem-manager.service                         loaded active       running                      Modem Manager
netfs.service                                 loaded active       exited                       LSB: Mount and unmount network filesystems.
NetworkManager.service                        loaded active       running                      Network Manager
ntpd.service                                  loaded maintenance  maintenance                  Network Time Service
polkitd.service                               loaded active       running                      Policy Manager
prefdm.service                                loaded active       running                      Display Manager
rc-local.service                              loaded active       exited                       /etc/rc.local Compatibility
rpcbind.service                               loaded active       running                      RPC Portmapper Service
rsyslog.service                               loaded active       running                      System Logging Service
rtkit-daemon.service                          loaded active       running                      RealtimeKit Scheduling Policy Service
sendmail.service                              loaded active       running                      LSB: start and stop sendmail
sshd@172.31.0.53:22-172.31.0.4:36368.service  loaded active       running                      SSH Per-Connection Server
sysinit.service                               loaded active       running                      System Initialization
systemd-logger.service                        loaded active       running                      systemd Logging Daemon
udev-post.service                             loaded active       exited                       LSB: Moves the generated persistent udev rules to /etc/udev/rules.d
udisks.service                                loaded active       running                      Disk Manager
upowerd.service                               loaded active       running                      Power Manager
wpa_supplicant.service                        loaded active       running                      Wi-Fi Security Service
avahi-daemon.socket                           loaded active       listening                    Avahi mDNS/DNS-SD Stack Activation Socket
cups.socket                                   loaded active       listening                    CUPS Printing Service Sockets
dbus.socket                                   loaded active       running                      dbus.socket
rpcbind.socket                                loaded active       listening                    RPC Portmapper Socket
sshd.socket                                   loaded active       listening                    sshd.socket
systemd-initctl.socket                        loaded active       listening                    systemd /dev/initctl Compatibility Socket
systemd-logger.socket                         loaded active       running                      systemd Logging Socket
systemd-shutdownd.socket                      loaded active       listening                    systemd Delayed Shutdown Socket
dev-disk-by\x1...x1db22a\x1d870f1adf2732.swap loaded active       active                       /dev/disk/by-uuid/fd626ef7-34a4-4958-b22a-870f1adf2732
basic.target                                  loaded active       active                       Basic System
bluetooth.target                              loaded active       active                       Bluetooth
dbus.target                                   loaded active       active                       D-Bus
getty.target                                  loaded active       active                       Login Prompts
graphical.target                              loaded active       active                       Graphical Interface
local-fs.target                               loaded active       active                       Local File Systems
multi-user.target                             loaded active       active                       Multi-User
network.target                                loaded active       active                       Network
remote-fs.target                              loaded active       active                       Remote File Systems
sockets.target                                loaded active       active                       Sockets
swap.target                                   loaded active       active                       Swap
sysinit.target                                loaded active       active                       System Initialization

LOAD   = Reflects whether the unit definition was properly loaded.
ACTIVE = The high-level unit activation state, i.e. generalization of SUB.
SUB    = The low-level unit activation state, values depend on unit type.
JOB    = Pending job for the unit.

221 units listed. Pass --all to see inactive units, too.
[root@lambda] ~#

（我已稍稍缩短输出，并删除与此贴无关的相关行）
看ACTIVE列，它输出了高端的服务状态（事实上，systemd维护的叫单元，它可以代表不止一种服务，但此事请听下回分解），分为active（运行），inactive（未运行），或其他状态。如果你仔细观察，你会发现列表中其中有一行被标记为maintenance并红色高亮。这提醒你该服务未能启动或者它报告了一个问题。在此例中为ntpd（网络时间服务）。现在让我们找出ntpd发生了什么，使用“systemctl status”命令。

[root@lambda] ~# systemctl status ntpd.service
ntpd.service - Network Time Service
Loaded: loaded (/etc/systemd/system/ntpd.service)
Active: maintenance
Main: 953 (code=exited, status=255)
CGroup: name=systemd:/systemd-1/ntpd.service
[root@lambda] ~#

它告诉我们ntpd在运行时被终止（PID=953），并准确告诉我们错误的原因：进程以错误码255而终止。
在后来的的systemd中，我们把它与ABRT相hook。然后，“systemctl status”如果输出一个服务崩溃了，它会直接显示ABRT的dump。

总结：使用“systemctl”和“systemctl status”命令作为一种更现代更完整的方式代替传统的SysV时代的启动信息。“systemctl status”不仅捕捉更详细的错误原因，同时显示运行时错误和启动错误。