autofs服務程序是一種Linux系統守護進程，當檢測到用戶試圖訪問一個尚未掛載的文件系統時，將自動掛載該文件系統。將信息填入/etc/fstab文件后，系統在每次開機時都自動將其掛載，而autofs服務程序則是在用戶需要使用該文件系統時才會動態掛載，從而節約了網絡資源和服務器硬件資源。
[root@study ~]# yum install autofs
Loaded plugins: fastestmirror
abc | 3.6 kB 00:00:00
Loading mirror speeds from cached hostfile
Resolving Dependencies
--> Running transaction check
---> Package autofs.x86_64 1:5.0.7-54.el7 will be installed
--> Processing Dependency: libtirpc.so.1()(64bit) for package: 1:autofs-5.0.7-54.el7.x86_64
--> Processing Dependency: libhesiod.so.0()(64bit) for package: 1:autofs-5.0.7-54.el7.x86_64
--> Running transaction check
---> Package hesiod.x86_64 0:3.2.1-3.el7 will be installed
---> Package libtirpc.x86_64 0:0.2.4-0.6.el7 will be installed
--> Finished Dependency Resolution
Dependencies Resolved
====================================================================================================================
Package Arch Version Repository Size
====================================================================================================================
Installing:
autofs x86_64 1:5.0.7-54.el7 abc 794 k
Installing for dependencies:
hesiod x86_64 3.2.1-3.el7 abc 30 k
libtirpc x86_64 0.2.4-0.6.el7 abc 85 k
Transaction Summary
====================================================================================================================
Install 1 Package (+2 Dependent packages)
Total download size: 908 k
Installed size: 5.3 M
Is this ok [y/d/N]: y
Downloading packages:
--------------------------------------------------------------------------------------------------------------------
Total 1.7 MB/s | 908 kB 00:00:00
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
Installing : hesiod-3.2.1-3.el7.x86_64 1/3
Installing : libtirpc-0.2.4-0.6.el7.x86_64 2/3
Installing : 1:autofs-5.0.7-54.el7.x86_64 3/3
Verifying : 1:autofs-5.0.7-54.el7.x86_64 1/3
Verifying : libtirpc-0.2.4-0.6.el7.x86_64 2/3
Verifying : hesiod-3.2.1-3.el7.x86_64 3/3
Installed:
autofs.x86_64 1:5.0.7-54.el7
Dependency Installed:
hesiod.x86_64 0:3.2.1-3.el7 libtirpc.x86_64 0:0.2.4-0.6.el7
Complete!
生產環境中的Linux服務器，會同時管理許多設備的掛載操作。如果把這些設備掛載信息寫入到autofs服務中的主配置文件中，會讓主配置文件繁雜，不利於服務執行效率，也不利於日后修改里面的配置內容，因此在autofs服務程序的主配置文件中需要按照“掛載目錄 子配置文件”的格式進行填寫。掛載目錄是設備掛載位置的上一級目錄。
[root@study ~]# vim /etc/auto.master
1 #
2 # Sample auto.master file
3 # This is a 'master' automounter map and it has the following format:
4 # mount-point [map-type[,format]:]map [options]
5 # For details of the format look at auto.master(5).
6 #
7 /media /etc/iso.misc
8 /misc /etc/auto.misc
9 #
10 # NOTE: mounts done from a hosts map will be mounted with the
11 # "nosuid" and "nodev" options unless the "suid" and "dev"
12 # options are explicitly given.
13 #
14 /net -hosts
15 #
16 # Include /etc/auto.master.d/*.autofs
17 # The included files must conform to the format of this file.
18 #
19 +dir:/etc/auto.master.d
20 #
21 # Include central master map if it can be found using
22 # nsswitch sources.
23 #
24 # Note that if there are entries for /net or /misc (as
25 # above) in the included master map any keys that are the
26 # same will not be seen as the first read key seen takes
27 # precedence.
28 #
29 +auto.master
在子配置文件中，按照“掛載目錄 掛載文件類型及權限：設備名稱”的格式進行填寫。例如要把光盤設備掛載到/media/iso目錄中，可將掛載目錄寫為iso，而-fstype為文件系統格式參數，iso9660為光盤設備格式，ro、nosuid及nodev為光盤設備具體的權限參數，/dev/cdrom則是定義要掛載的設備名稱。
[root@study ~]# vim /etc/iso.misc
[root@study ~]# systemctl start autofs
[root@study ~]# systemctl enable autofs
Created symlink from /etc/systemd/system/multi-user.target.wants/autofs.service to /usr/lib/systemd/system/autofs.service.
接下來會發現，查看當前光盤設備掛載情況，光盤設備沒有被掛載上，而且/media目錄也沒有iso子目錄，但是可以用cd命令切換到這個iso子目錄，而且光盤設備會立即被掛載上。
[root@study ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos-root 18G 2.8G 15G 17% /
devtmpfs 479M 0 479M 0% /dev
tmpfs 489M 0 489M 0% /dev/shm
tmpfs 489M 6.7M 483M 2% /run
tmpfs 489M 0 489M 0% /sys/fs/cgroup
/dev/sda1 497M 125M 373M 25% /boot
tmpfs 98M 0 98M 0% /run/user/0
[root@study ~]# cd /media/
[root@study media]# ls
[root@study media]# cd iso
[root@study iso]# ls -l
total 1490
-r--r--r-- 1 root root 14 Dec 9 2015 CentOS_BuildTag
dr-xr-xr-x 3 root root 2048 Dec 9 2015 EFI
-r--r--r-- 1 root root 215 Dec 9 2015 EULA
-r--r--r-- 1 root root 18009 Dec 9 2015 GPL
dr-xr-xr-x 3 root root 2048 Dec 9 2015 images
dr-xr-xr-x 2 root root 2048 Dec 9 2015 isolinux
dr-xr-xr-x 2 root root 2048 Dec 9 2015 LiveOS
dr-xr-xr-x 2 root root 1486848 Dec 9 2015 Packages
dr-xr-xr-x 2 root root 4096 Dec 9 2015 repodata
-r--r--r-- 1 root root 1690 Dec 9 2015 RPM-GPG-KEY-CentOS-7
-r--r--r-- 1 root root 1690 Dec 9 2015 RPM-GPG-KEY-CentOS-Testing-7
-r--r--r-- 1 root root 2883 Dec 9 2015 TRANS.TBL
[root@study iso]# cd
[root@study ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/centos-root 18G 2.8G 15G 17% /
devtmpfs 479M 0 479M 0% /dev
tmpfs 489M 0 489M 0% /dev/shm
tmpfs 489M 6.7M 483M 2% /run
tmpfs 489M 0 489M 0% /sys/fs/cgroup
/dev/sda1 497M 125M 373M 25% /boot
tmpfs 98M 0 98M 0% /run/user/0
/dev/sr0 7.3G 7.3G 0 100% /media/iso