1241899SdteskeThis menu allows you to configure the Securelevel mechanism in FreeBSD. 2241899Sdteske 3241899SdteskeSecurelevels may be used to limit the privileges assigned to the 4241899Sdteskeroot user in multi-user mode, which in turn may limit the effects of 5241899Sdteskea root compromise, at the cost of reducing administrative functions. 6241899SdteskeRefer to the security(7) and init(8) manual pages for complete details. 7241899Sdteske 8241899Sdteske -1 Permanently insecure mode - always run the system in level 0 9241899Sdteske mode. This is the default initial value. 10241899Sdteske 11241899Sdteske 0 Insecure mode - immutable and append-only flags may be turned 12241899Sdteske off. All devices may be read or written subject to their 13241899Sdteske permissions. 14241899Sdteske 15241899Sdteske 1 Secure mode - the system immutable and system append-only 16241899Sdteske flags may not be turned off; disks for mounted file systems, 17241899Sdteske /dev/mem, /dev/kmem and /dev/io (if your platform has it) 18241899Sdteske may not be opened for writing; kernel modules (see kld(4)) 19241899Sdteske may not be loaded or unloaded. 20241899Sdteske 21241899Sdteske 2 Highly secure mode - same as secure mode, plus disks may not 22241899Sdteske be opened for writing (except by mount(2)) whether mounted or 23241899Sdteske not. This level precludes tampering with file systems by 24241899Sdteske unmounting them, but also inhibits running newfs(8) while the 25241899Sdteske system is multi-user. 26241899Sdteske 27241899Sdteske In addition, kernel time changes are restricted to less than 28241899Sdteske or equal to one second. Attempts to change the time by more 29241899Sdteske than this will log the message ``Time adjustment clamped to +1 30241899Sdteske second''. 31241899Sdteske 32241899Sdteske 3 Network secure mode - same as highly secure mode, plus IP 33241899Sdteske packet filter rules (see ipfw(8), ipfirewall(4) and pfctl(8)) 34241899Sdteske cannot be changed and dummynet(4) or pf(4) configuration 35241899Sdteske cannot be adjusted. 36241899Sdteske 37241899SdteskeSecurelevels must be used in combination with careful system design and 38241899Sdteskeapplication of protective mechanisms to prevent system configuration 39241899Sdteskefiles from being modified in a way that compromises the protections of 40241899Sdteskethe securelevel variable upon reboot. 41