在当前用户下的.bashrc 中加一行:

export PATH=".:/bin:/sbin:/usr/sbin:/usr/bin:/usr/local/bin:/usr/X11R6/bin"

然后
#source .bashrc

有些命令即便能调用,也不会出现任何信息,或者要输入root密码的,说明要以超级权限运行的;

比如

[beinan@localhost ~]$ fdisk -l
[beinan@localhost ~]$ su
Password:
[root@localhost beinan]# fdisk -l
Disk /dev/hda: 80.0 GB, 80026361856 bytes
255 heads, 63 sectors/track, 9729 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/hda1 * 1 765 6144831 7 HPFS/NTFS
/dev/hda2 766 2805 16386300 c W95 FAT32 (LBA)
/dev/hda3 2806 7751 39728745 5 Extended
/dev/hda5 2806 3825 8193118+ 83 Linux
/dev/hda6 5101 5198 787153+ 82 Linux swap / Solaris
[root@localhost beinan]#