http://0pointer.de/blog/projects/systemd-for-admins-1.html

就像很多人知道的那样, systemd是新版本fedora(从F14开始)的init系统, 它也正在被一些其它的发行版所采用(例如, OpenSuse).

对系统管理员来说,systmed提供了许多新的特性,并在本质上改变和加强了系统管理过程.

这篇博客是系列文章的第一部分, 在接下来的几个月我打算差不多每周写一篇.

每篇文章我将尝试解释systemd的一个新的特性. 其实它的许多特性都很小很简单, 所以这个系列应该会使很多读者感兴趣. 

当然有时,我也会深挖systemd提供给你的一些伟大的新特性.

Verifying Bootup

传统的 linux系统在启动过程中, 你看到大量的短信息从你的屏幕上滚过.systemd中, 随着我们改进启动速度并使启动过程并行化, 这些信息的显示时间越来越短, 而且可读性也越来越差了, 就如同你在某些像Plymouth那样提供图像启动画面的启动程序中看到的那样.尽管它仍然提供了有用的相关性信息, 它在启动过程中记录了每个服务的开始,是否成功或失败(绿色[OK]代表成功,红色FAILED代表失败].

为了在提高机器启动速度并使启动过程并行执行的同时, 让启动的信息在运行时更友好,我们为systemd增加了一个新的特性,用来在启动时和运行时跟踪并记录每个服务是否启动成功, 是否以非0值退出, 是否超时, 是否非正常终止(被段错误信号或类似的东西), 只是在shell下简单的敲systemdctl, 你就能查询所有服务的状态, 无论是systemd的还是SysV/LSB的服务

[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] ~#

(我缩短了一些输出,移除了一些与此篇博客无关的行)

看一下ACTIVE列, 显示了一个服务(或者任何systemd维护的单元, 可以不只是服务,我们在后续文章中可以看到)的最基本的状态, 可能是active状态(比如: running), 可能是incative(比如: not running))也可能是其他状态.如果仔细看你会发现有一项标记为maintenance,红色高亮. 这提示你这个服务运行失败或者碰到其他问题.本例中是ntpd.现在让我们通过systemdctl status命令看看ntpd到底发生了什么. 

[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] ~#

这告知我们NTPzai运行时终止了(它运行时的PID是953), 并告诉我们确切的出错条件:进程以状态码255退出.

以后的systmed版本中,我们计划把这种情况做成钩子,连接ABRT(自动bug报告工具). 这样,如果systemctl status告诉你一个服务崩溃了, 它将指示给你在ABRT中确切的崩溃dump内容

总结: 用systemctl和systemctl status作为传统SysV启动信息的代替工具, 更现代,更完备.system status不但能捕获更多的出错细节, 还能在提供启动错误信息的同时提供运行时错误信息

下周见