查询当前有哪些文件系统可用，使用df命令：
sudo df
返回的结果类似下面：
文件系统 1K-块 已用 可用 已用% 挂载点 /dev/sda5 19465264 4360132 14128648 24% / udev 1007588 12 1007576 1% /dev tmpfs 406552 900 405652 1% /run none 5120 0 5120 0% /run/lock none 1016372 548 1015824 1% /run/shm /dev/sda1 192534 59009 123797 33% /boot /dev/sda7 97502732 5979672 86640324 7% /home /dev/sda6 29223512 2279036 25479696 9% /usr/local
df命令的结果实际上就是/etc/mtab文件的内容。/etc/mtab文件记录的是成功挂载后所有文件系统的信息。
/dev/sda5 / ext4 rw,errors=remount-ro 0 0 proc /proc proc rw,noexec,nosuid,nodev 0 0 sysfs /sys sysfs rw,noexec,nosuid,nodev 0 0 none /sys/fs/fuse/connections fusectl rw 0 0 none /sys/kernel/debug debugfs rw 0 0 none /sys/kernel/security securityfs rw 0 0 udev /dev devtmpfs rw,mode=0755 0 0 devpts /dev/pts devpts rw,noexec,nosuid,gid=5,mode=0620 0 0 tmpfs /run tmpfs rw,noexec,nosuid,size=10%,mode=0755 0 0 none /run/lock tmpfs rw,noexec,nosuid,nodev,size=5242880 0 0 none /run/shm tmpfs rw,nosuid,nodev 0 0 /dev/sda1 /boot ext4 rw 0 0 /dev/sda7 /home ext4 rw 0 0 /dev/sda6 /usr/local ext4 rw 0 0 gvfs-fuse-daemon /home/amonest/.gvfs fuse.gvfs-fuse-daemon rw,nosuid,nodev,user=amonest 0 0
/etc目录下还有一个fstab文件，规定了哪些分区是开机后可以直接挂载的。
# /etc/fstab: static file system information. # # Use 'blkid' to print the universally unique identifier for a # device; this may be used with UUID= as a more robust way to name devices # that works even if disks are added and removed. See fstab(5). # # <file system> <mount point> <type> <options> <dump> <pass> proc /proc proc nodev,noexec,nosuid 0 0 # / was on /dev/sda5 during installation UUID=3e2ffdd5-b780-4705-8b91-e22f429cd256 / ext4 errors=remount-ro 0 1 # /boot was on /dev/sda1 during installation UUID=5e879318-93cb-4ea7-842f-18ba7e7964cb /boot ext4 defaults 0 2 # /home was on /dev/sda7 during installation UUID=d097dbe5-fdc6-475c-bad4-1a11200f7fec /home ext4 defaults 0 2 # /usr/local was on /dev/sda6 during installation UUID=1d7fbe50-5cb6-4584-87da-024353d8af56 /usr/local ext4 defaults 0 2 # swap was on /dev/sda8 during installation UUID=f540049d-5049-4963-a069-49e05060aed0 none swap sw 0 0
从/etc/fstab可以看到，Ubuntu中，每个分区都有一个UUID与之对应。可以使用blkid查询每个分区的UUID。
sudo blkid
返回的结果类似下面：
/dev/sda1: UUID="5e879318-93cb-4ea7-842f-18ba7e7964cb" TYPE="ext4" /dev/sda5: UUID="3e2ffdd5-b780-4705-8b91-e22f429cd256" TYPE="ext4" /dev/sda6: UUID="1d7fbe50-5cb6-4584-87da-024353d8af56" TYPE="ext4" /dev/sda7: UUID="d097dbe5-fdc6-475c-bad4-1a11200f7fec" TYPE="ext4" /dev/sda8: UUID="f540049d-5049-4963-a069-49e05060aed0" TYPE="swap"
也可以通过直接查询/etc/blkid.tab文件得到：
<device DEVNO="0x0801" TIME="1339507071.210539" UUID="5e879318-93cb-4ea7-842f-18ba7e7964cb" TYPE="ext4">/dev/sda1</device> <device DEVNO="0x0805" TIME="1339507071.210708" UUID="3e2ffdd5-b780-4705-8b91-e22f429cd256" TYPE="ext4">/dev/sda5</device> <device DEVNO="0x0806" TIME="1339507071.210828" UUID="1d7fbe50-5cb6-4584-87da-024353d8af56" TYPE="ext4">/dev/sda6</device> <device DEVNO="0x0807" TIME="1339507071.210943" UUID="d097dbe5-fdc6-475c-bad4-1a11200f7fec" TYPE="ext4">/dev/sda7</device> <device DEVNO="0x0808" TIME="1339507071.211068" UUID="f540049d-5049-4963-a069-49e05060aed0" TYPE="swap">/dev/sda8</device>
查询某个目录的空间使用情况，可以使用du命令：
sudo du -h --max-depth=1 /usr/local | sort -h
返回的结果类似下面：
4.0K /usr/local/bin 4.0K /usr/local/etc 4.0K /usr/local/games 4.0K /usr/local/include 4.0K /usr/local/sbin 16K /usr/local/lib 16K /usr/local/lost+found 60K /usr/local/share 410M /usr/local/src 1.3G /usr/local/development 1.7G /usr/local