haldaemon服务描述

Linux 硬件抽象层 (HAL) 实现了系统上所有硬件的连贯描述，包括 USB（通用串行总线）等热插拔设备。
它的工作原理是合并操作系统、物理硬件、设备驱动程序、子系统（例如 CUPS（通用 Unix 打印系统））甚至来自系统管理员的信息。
该信息被整理并通过 HAL 编程接口提供给应用程序。

haldaemon 服务调用HAL 守护进程hald 通过内核D-BUS 通信通道获取内核级数据，收集并分发这些信息。
设备数据以键+值属性对的形式呈现。

HAL 服务的一个客户端是 fstab-sync(8) 工具，它自动更新 /etc/fstab 以响应磁盘驱动器联机。
这仅适用于 CentOS/RHEL 4.
fatab-sync 工具已被禁用，并在 CentOS/RHEL 5 上引入了新的挂载支持。

配置

要管理 haldaemon 服务以供将来关闭和重新启动，请使用 chkconfig 工具：

# /sbin/chkconfig haldaemon on
# /sbin/chkconfig --list haldaemon
haldaemon 0:off 1:off 2:on 3:on 4:on 5:on 6:off

要立即控制 haldaemon 服务，请使用服务工具：

# /sbin/servie haldaemon
Uage: /etc/init.d/haldaemon {start|stop|status|restart|condrestart}

启动或者停止守护进程：

# /sbin/service haldaemon start
Starting HAL daemon:                                       [  OK  ]
# /sbin/service haldaemon stop
Stopping HAL daemon:                                       [  OK  ]

RPM 包名：hal

e.g. hal-0.5.8.1-38.el5.i386

一旦此守护程序服务（haldaemon）运行，就可以使用实用程序“lshal”列出设备及其属性。
例如：

# lshal
Dumping 49 device(s) from the Global Device List:
------------------------------------------------
udi = '/org/freedesktop/Hal/devices/pci_8086_2770'
info.parent = '/org/freedesktop/Hal/devices/computer' (string)
info.udi = '/org/freedesktop/Hal/devices/pci_8086_2770' (string)
pci.device_protocol = 0 (0x0) (int)
pci.device_subclass = 0 (0x0) (int)
pci.device_class = 6 (0x6) (int)
info.vendor = 'Intel Corporation' (string)
info.product = '82945G/GZ/P/PL Memory Controller Hub' (string)
pci.subsys_vendor = 'Dell' (string)
pci.product = '82945G/GZ/P/PL Memory Controller Hub' (string)
pci.vendor = 'Intel Corporation' (string)
pci.subsys_product_id = 429 (0x1ad) (int)
pci.subsys_vendor_id = 4136 (0x1028) (int)
pci.product_id = 10096 (0x2770) (int)
pci.vendor_id = 32902 (0x8086) (int)
pci.linux.sysfs_path = '/sys/devices/pci0000:00/0000:00:00.0' (string)
linux.sysfs_path_device = '/sys/devices/pci0000:00/0000:00:00.0' (string)
linux.sysfs_path = '/sys/devices/pci0000:00/0000:00:00.0' (string)
info.bus = 'pci' (string)
... ...

haldaemon 可以使用以下文件进行最低限度的配置：

/etc/hal/hald.conf

它是一个 XML 文件。
例如：

<?xml version="1.0" encoding="ISO-8859-1"?> <!-- -*- SGML -*- -->
<!-- This configuration file controls the Hardware Abstraction Layer
     daemon - it is meant that OS vendors customize this file to reflect
     their desired policy.
  -->
<haldconfig>
  <!-- If true, then the device list is saved to disk such that
       properties are kept between invocations of hald.
    -->
  <persistent_device_list>false</persistent_device_list>
  <!-- Default value for storage.media_check_enabled for devices of
       capability storage - this can be overridden by .fdi files.
       Setting this to false results a whitelist policy, e.g. media
       check is only enabled for storage devices with a .fdi file
       saying so.
       Conversely, setting it to true results in a blacklist policy
       where media check is enabled by default but may be overridden
       by a .fdi for devices causing trouble.
  -->
  <storage_media_check_enabled>true</storage_media_check_enabled>

  <!-- Default value for storage.automount_enabled_hint for devices of
       capability storage - this can be overridden by .fdi files.
       Setting this to false results a whitelist policy, e.g. policy
       agents should only automount storage devices with a .fdi file
       saying so.
       Conversely, setting it to true results in a blacklist policy
       where policy agents should always automount unless this is
 explicitly overridden by .fdi for devices causing trouble.
  -->
  <storage_automount_enabled_hint>true</storage_automount_enabled_hint>
</haldconfig>