运行级别对于系统使用来说应该是一个很重要的基本概念，原来一直使用Linux，现在又用Solaris和AIX，一下模糊了，他们对runlevel的定义有些许不同，现本人搜集了哈，做个比较。
| runlevel | Linux | Solaris |
| 0 | halt (Do NOT set initdefault to /etc/inittal "initlevel" entry) | halt |
| 1 | Single user mode | Single user mode |
| 2 | Multiuser, without NFS (The same as 3, if you do not have networking) | multiuser, unshare net |
| 3 | Full multiuser mode | multiuser, deafult |
| 4 | unused | unused |
| 5 | X11 | halt, power off |
| 6 | reboot (Do NOT set initdefault to this) | reboot to level 3 |
| S | None | equal “init 1”, “boot -s” |
AIX:
"AIX does not follow the System V R4 (SVR4) run level specification, with run levels from 0 to 9 available, as well as from a to c. 0 and 1 are reserved, 2 is the default normal multiuser mode and run levels from 3 to 9 are free to be defined by the administrator. Run levels from a to c allow the execution of processes in that run level without killing processes started in another."
本来想把上个表格做得更全些的，结果在google上一搜，晕！人家[url]http:///wiki/Runlevel[/url]做得之巴适！我晕！真是众人拾柴火焰高啊！大家还是有空多去看看wikipedia吧！
