一.查看内存信息
可以使用free命令显示系统的物理内存和交换分区的总量，以及已使用的、空闲的、共享的、在内核缓冲内的和被缓存的内存数量。
使用free命令可以显示计算机系统的内存容量。
[root@redhat2 ~]# free --help
free: invalid option -- '-'
usage: free [-b|-k|-m|-g] [-l] [-o] [-t] [-s delay] [-c count] [-V]
-b,-k,-m,-g show output in bytes, KB, MB, or GB
-l show detailed low and high memory statistics
-o use old format (no -/+buffers/cache line)
-t display total for RAM + swap
-s update every [delay] seconds
-c update [count] times
-V display version information and exit
[root@redhat2 ~]#
例1：查看系统的物理内存和交换分区的总量。
[root@redhat2 ~]# free
total used free shared buffers cached
Mem: 1592280 368792 1223488 0 51824 122532
-/+ buffers/cache: 194436 1397844
Swap: 3211256 0 3211256
[root@redhat2 ~]#
例2：以MB为单位查看系统的物理内存和交换分区的总量。
[root@redhat2 ~]# free -m
total used free shared buffers cached
Mem: 1554 360 1194 0 50 119
-/+ buffers/cache: 189 1365
Swap: 3135 0 3135
[root@redhat2 ~]#
例3：显示物理内存和交换分区的总和。
[root@redhat2 ~]# free -t
total used free shared buffers cached
Mem: 1592280 368792 1223488 0 51880 122532
-/+ buffers/cache: 194380 1397900
Swap: 3211256 0 3211256
Total: 4803536 368792 4434744
二.查看磁盘空间占用情况
使用df命令可以显示磁盘的相关信息。检查文件系统的磁盘空间占用情况，利用该命令获取硬盘占用了多少空间、目前还剩下多少空间等相关信息。
[root@redhat2 ~]# df --help
Usage: df [OPTION]... [FILE]...
Show information about the file system on which each FILE resides,
or all file systems by default.
Mandatory arguments to long options are mandatory for short options too.
-a, --all include dummy file systems
-B, --block-size=SIZE use SIZE-byte blocks
--direct show statistics for a file instead of mount point
--total produce a grand total
-h, --human-readable print sizes in human readable format (e.g., 1K 234M 2G)
-H, --si likewise, but use powers of 1000 not 1024
-i, --inodes list inode information instead of block usage
-k like --block-size=1K
-l, --local limit listing to local file systems
--no-sync do not invoke sync before getting usage info (default)
-P, --portability use the POSIX output format
--sync invoke sync before getting usage info
-t, --type=TYPE limit listing to file systems of type TYPE
-T, --print-type print file system type
-x, --exclude-type=TYPE limit listing to file systems not of type TYPE
-v (ignored)
--help display this help and exit
--version output version information and exit
例1:显示系统的磁盘空间使用量。
[root@redhat2 ~]# df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sda3 27499388 6662112 19440388 26% /
tmpfs 796140 88 796052 1% /dev/shm
/dev/sda1 297485 33069 249056 12% /boot
[root@redhat2 ~]#
例2：以MB或GB为单位显示系统的磁盘空间使用量。
[root@redhat2 ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda3 27G 6.4G 19G 26% /
tmpfs 778M 88K 778M 1% /dev/shm
/dev/sda1 291M 33M 244M 12% /boot
[root@redhat2 ~]#
例3：显示ext4文件系统类型磁盘空间使用量。
[root@redhat2 ~]# df -t ext4
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sda3 27499388 6662112 19440388 26% /
/dev/sda1 297485 33069 249056 12% /boot
[root@redhat2 ~]#
例4：以MB或GB为单位显示磁盘空间使用量时也显示文件系统类型。
[root@redhat2 ~]# df -hT
Filesystem Type Size Used Avail Use% Mounted on
/dev/sda3 ext4 27G 6.4G 19G 26% /
tmpfs tmpfs 778M 88K 778M 1% /dev/shm
/dev/sda1 ext4 291M 33M 244M 12% /boot
[root@redhat2 ~]#
例5：显示磁盘空间i节点使用情况。
[root@redhat2 ~]# df -i
Filesystem Inodes IUsed IFree IUse% Mounted on
/dev/sda3 1746240 107517 1638723 7% /
tmpfs 199035 3 199032 1% /dev/shm
/dev/sda1 76912 39 76873 1% /boot
[root@redhat2 ~]#
三.显示目录或文件的大小
使用du命令可以显示目录或文件的大小。
[root@redhat2 ~]# du --help
Usage: du [OPTION]... [FILE]...
or: du [OPTION]... --files0-from=F
Summarize disk usage of each FILE, recursively for directories.
Mandatory arguments to long options are mandatory for short options too.
-a, --all write counts for all files, not just directories
--apparent-size print apparent sizes, rather than disk usage; although
the apparent size is usually smaller, it may be
larger due to holes in (`sparse') files, internal
fragmentation, indirect blocks, and the like
-B, --block-size=SIZE use SIZE-byte blocks
-b, --bytes equivalent to `--apparent-size --block-size=1'
-c, --total produce a grand total
-D, --dereference-args dereference only symlinks that are listed on the
command line
--files0-from=F summarize disk usage of the NUL-terminated file
names specified in file F;
If F is - then read names from standard input
-H equivalent to --dereference-args (-D)
-h, --human-readable print sizes in human readable format (e.g., 1K 234M 2G)
--si like -h, but use powers of 1000 not 1024
-k like --block-size=1K
-l, --count-links count sizes many times if hard linked
-m like --block-size=1M
-L, --dereference dereference all symbolic links
-P, --no-dereference don't follow any symbolic links (this is the default)
-0, --null end each output line with 0 byte rather than newline
-S, --separate-dirs do not include size of subdirectories
-s, --summarize display only a total for each argument
-x, --one-file-system skip directories on different file systems
例1：显示文件/root/a.sh的大小。
[root@redhat2 ~]# du /root/a.sh
4 /root/a.sh
[root@redhat2 ~]#
[root@redhat2 ~]# du -h a.sh
4.0K a.sh
[root@redhat2 ~]#