- Advance Praise for Absolute OpenBSD, 2nd Edition
- Dedication
- About the Author
- About the Technical Reviewer
- Foreword
- Acknowledgments
- Introduction
- 1. Getting Additional Help
- 2. Installation Preparations
- 3. Installation Walk-Through
- 4. Post-Install Setup
- 5. The Boot Process
- 6. User Management
- 7. Root, and How to Avoid It
- The Root Password
- Using Groups
- Hiding Root with sudo
- Using sudo
- sudoedit
- The Biggest sudo Mistake: Exclusions
- sudo Logs
- 8. Disks and Filesystems
- Device Nodes
- DUIDs and /etc/fstab
- MBR Partitions and fdisk(8)
- Labeling Disks
- The Fast File System
- What’s Currently Mounted?
- Mounting and Unmounting Partitions
- How Full Is That Partition?
- Adding New Hard Disks
- 9. More Filesystems
- 10. Securing Your System
- 11. Overview of TCP/IP
- 12. Connecting to the Network
- 13. Software Management
- 14. Everything /etc
- /etc Across Unix Variants
- The /etc Files
- /etc/adduser.conf
- /etc/amd
- /etc/authpf
- /etc/bgpd.conf
- /etc/boot.conf
- /etc/changelist
- /etc/chio.conf
- /etc/csh.*
- /etc/daily and /etc/daily.local
- /etc/dhclient.conf
- /etc/dhcpd.conf
- /etc/disklabels/
- /etc/disktab
- /etc/dumpdates
- /etc/dvmrpd.conf
- /etc/exports
- /etc/fbtab
- /etc/firmware
- /etc/fonts/
- /etc/fstab
- /etc/ftpchroot
- /etc/ftpusers
- /etc/gettytab
- /etc/group
- /etc/hostapd.conf
- /etc/hostname.*
- /etc/hosts
- /etc/hosts.equiv
- /etc/hosts.lpd
- /etc/hotplug/
- /etc/ifstated.conf
- /etc/iked/, /etc/iked.conf, /etc/ipsec.conf, and /etc/isakmpd
- /etc/inetd.conf
- /etc/kbdtype
- /etc/kerberosV/
- /etc/ksh.kshrc
- /etc/ldap/ and /etc/ldapd.conf
- /etc/localtime
- /etc/locate.rc
- /etc/login.conf
- /etc/lynx.cfg
- /etc/magic
- /etc/mail/
- /etc/mail.rc
- /etc/mailer.conf
- /etc/man.conf
- /etc/master.passwd, /etc/passwd, /etc/spwd.db, and /etc/pwd.db
- /etc/mixerctl.conf
- /etc/mk.conf
- /etc/moduli
- /etc/monthly and /etc/monthly.local
- /etc/motd
- /etc/mrouted.conf
- /etc/mtree/
- /etc/mygate
- /etc/myname
- /etc/netstart
- /etc/networks
- /etc/newsyslog.conf
- /etc/nginx/
- /etc/nsd.conf
- /etc/ntpd.conf
- /etc/ospf6d.conf and /etc/ospfd.conf
- /etc/pf.conf and /etc/pf.os
- /etc/ppp/
- /etc/printcap
- /etc/protocols
- /etc/rbootd.conf
- /etc/rc.*
- /etc/relayd.conf
- /etc/remote
- /etc/resolv.conf and /etc/resolv.conf.tail
- /etc/ripd.conf
- /etc/rmt
- /etc/rpc
- /etc/sasyncd.conf
- /etc/sensorsd.conf
- /etc/services
- /etc/shells
- /etc/skel/
- /etc/sliphome/
- /etc/snmpd.conf
- /etc/ssh/
- /etc/ssl/
- /etc/sudoers
- /etc/sysctl.conf
- /etc/syslog.conf
- /etc/systrace/
- /etc/termcap
- /etc/ttys
- /etc/weekly and /etc/weekly.local
- /etc/wsconsctl.conf
- /etc/X11
- /etc/ypldap.conf
- 15. System Maintenance
- 16. Network Servers
- 17. Desktop OpenBSD
- 18. Kernel Configuration
- 19. Building Custom Kernels
- 20. Upgrading
- 21. Packet Filtering
- 22. Advanced PF
- 23. Customizing OpenBSD
- A. Afterword
- Index
- About the Author
- Copyright
Booting in Single-User Mode
Single-user mode is the earliest point when OpenBSD can give you a Unix-style shell prompt. At this point, the kernel has probed all the hardware, attached drivers to all the hardware that it’s going to acknowledge, and started init. The system hasn’t mounted any filesystems except for the root partition, which is mounted in read-only mode. The network isn’t started, no services are running, security is not implemented, and filesystem permissions are ignored.
To boot OpenBSD in single-user mode, enter boot -s at the loader prompt.
boot> boot -s
Why would you want to boot into single-user mode? If your computer has a problem that is preventing it from booting, you should be able to access single-user mode and fix the problem. Suppose a failed disk is preventing the system from booting during a multiuser boot, or you changed your terminal settings in /etc/ttys and now you can’t log on to the system. Or maybe you put a daft setting in rc.conf.local, and the boot process hangs because it’s trying to do something impossible. At times like these, single-user mode is your best friend.
Also, some system administration tasks, such as clearing filesystem flags (see Chapter 8), can be done only in single-user mode.
Mounting Disks in Single-User Mode
Usually, you should have a fully functional filesystem before doing anything in single-user mode. If your system crashed, be sure to check the integrity of your filesystems before mounting them:
# fsck -p /dev/sd0a (e4bf0318329fe596.a): file system is clean; not checking /dev/sd0h (e4bf0318329fe596.h): file system is clean; not checking … # mount -a
fsck and mount have many more options. We’ll cover them in more detail in Chapter 8.
Once you’ve mounted all of your filesystems, all usual command-line software should be available. You should be able to edit configuration files, start and stop programs, and generally do whatever you like to the system (including destroy it).
Starting the Network in Single-User Mode
Use the shell script /etc/netstart to configure the network while in singleuser mode. (You could run all the appropriate commands by hand, but /etc/netstart will read your system’s configuration files and do the grunt work for you.) You must explicitly run this script through sh:
# sh /etc/netstart
If you’re booting into single-user mode because of network problems, this script will conveniently reproduce the issue for you.
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