1224093SdougbThis menu allows you to configure the Securelevel mechanism in FreeBSD. 2224093Sdougb 3224093SdougbSecurelevels may be used to limit the privileges assigned to the 4224093Sdougbroot user in multi-user mode, which in turn may limit the effects of 5224093Sdougba root compromise, at the cost of reducing administrative functions. 6224093SdougbRefer to the security(7) and init(8) manual pages for complete details. 7224093Sdougb 8224093Sdougb -1 Permanently insecure mode - always run the system in level 0 9224093Sdougb mode. This is the default initial value. 10224093Sdougb 11224093Sdougb 0 Insecure mode - immutable and append-only flags may be turned 12224093Sdougb off. All devices may be read or written subject to their 13224093Sdougb permissions. 14224093Sdougb 15224093Sdougb 1 Secure mode - the system immutable and system append-only 16224093Sdougb flags may not be turned off; disks for mounted file systems, 17224093Sdougb /dev/mem, /dev/kmem and /dev/io (if your platform has it) 18224093Sdougb may not be opened for writing; kernel modules (see kld(4)) 19224093Sdougb may not be loaded or unloaded. 20224093Sdougb 21224093Sdougb 2 Highly secure mode - same as secure mode, plus disks may not 22224093Sdougb be opened for writing (except by mount(2)) whether mounted or 23224093Sdougb not. This level precludes tampering with file systems by 24224093Sdougb unmounting them, but also inhibits running newfs(8) while the 25 system is multi-user. 26 27 In addition, kernel time changes are restricted to less than 28 or equal to one second. Attempts to change the time by more 29 than this will log the message ``Time adjustment clamped to +1 30 second''. 31 32 3 Network secure mode - same as highly secure mode, plus IP 33 packet filter rules (see ipfw(8), ipfirewall(4) and pfctl(8)) 34 cannot be changed and dummynet(4) or pf(4) configuration 35 cannot be adjusted. 36 37Securelevels must be used in combination with careful system design and 38application of protective mechanisms to prevent system configuration 39files from being modified in a way that compromises the protections of 40the securelevel variable upon reboot. 41