DESCRIPTION¶
This manual page was written for the Debian GNU/Linux distribution because the original program does not have a manual page. Check linux —help for an up-to-date synopsis.
OPTIONS¶
debugtrace Causes the tracing thread to pause until it is attached by a debugger and continued. This is mostly for debugging crashes early during boot, and should be pretty much obsoleted by the debug switch.
honeypot This makes UML put process stacks in the same location as they are on the host, allowing exploits such as stack smashes to work against UML.
debug Starts up the kernel under the control of gdb. See the kernel debugging tutorial and the debugging session pages in the user-mode-linux-doc package for more information.
To use hostfs for the root filesystem, use the syntax «root=/dev/root rootflags=/ rootfstype=hostfs»
jail Enables the protection of kernel memory from processes
tty This will make UML attach the device to the specified tty. If the tty that you specify is the slave end of a tty/pty pair, something else must have already opened the corresponding pty in order for this to work.
pty This will cause UML to allocate a free host pty for the device. The pty will be announced in the boot log. You would attach to it via the corresponding tty.
pts terminal This is similar to pty above, but the specified UML device will be attached to a free pts device on the host. Look at the boot log to see which one.
xterm UML will run an xterm and the device will be attached to it.
file descriptors If you set up a file descriptor on the UML command line, you can attach a UML device to it. This is most commonly used to put the main console back on stdin and stdout after assigning all the other consoles to something else.
You can also specify different input and output channels for a device by putting a comma between them:
See Setting up Serial Lines and Consoles (link to URL file:///usr/share/doc/user-mode-linux-doc/html/input.html) for a more information.
fake_ide Create ide0 entries that map onto ubd devices.
ubd0r=/tmp/debian-woody.ext2
ubd0rs=/tmp/debian-woody.ext2
This is used to associate a device with a file or in the underlying filesystem. Usually, there is a filesystem in the file, but that’s not required. Swap devices containing swap files can be specified like this. Also, a file which doesn’t contain a filesystem can have its contents read in the virtual machine by running dd on the device. Appending an ‘r’ will cause that device to be mounted read-only. Appending an ‘s’ tells UML to open the file using O_SYNC (synchronous I/O).
The ubd option can no longer be used to specify a hostfs root filesystem. See the «root» option for a more correct method.
udb This option is here solely to catch ubd -> udb typos, which can be to impossible to catch visually unless you specifically look for them. The only result of any option starting with ‘udb’ is an error in the boot output.
fakehd Change the ubd device name to «hd», allowing programs within UML to access UBD devices as if they were normal IDE disks.
eth0=ethertap,tap0,,192.168.0.1
eth2+=tuntap,,ethernet_address,ip_address
eth0=tuntap,,fe:fd:0:0:0:1,192.168.0.1
eth6+=daemon,ethernet_address,type,control_socket,data_socket
eth0=daemon,,unix,/var/run/uml-utilities/uml_switch.ctl
eth9+=mcast,ethernet_address,address,port,ttl
mode=tt When both CONFIG_MODE_TT and CONFIG_MODE_SKAS are enabled, this option forces UML to run in tt (tracing thread) mode. It is not the default because it’s slower and less secure than skas mode.
mode=skas0 Disables SKAS3 usage, so that SKAS0 is used, unless you specify mode=tt. Note that this was recently added — on older kernels you must use simply «skas0».
skas0 Disables SKAS3 usage, so that SKAS0 is used, unless you specify mode=tt.
mconsole=notify:socket Requests that the mconsole driver send a message to the named Unix socket containing the name of the mconsole socket. This also serves to notify outside processes when UML has booted far enough to respond to mconsole requests.
aio=2.4 This is used to force UML to use 2.4-style AIO even when 2.6 AIO is available. 2.4 AIO is a single thread that handles one request at a time, synchronously. 2.6 AIO is a thread which uses the 2.6 AIO interface to handle an arbitrary number of pending requests. 2.6 AIO is not available in tt mode, on 2.4 hosts, or when UML is built with /usr/include/linux/aio_abi.h not available. Many distributions don’t include aio_abi.h, so you will need to copy it from a kernel tree to your /usr/include/linux in order to build an AIO-capable UML.
noptraceldt Turns off usage of PTRACE_LDT, even if host supports it. To support PTRACE_LDT, the host needs to be patched using the current skas3 patch.
noptracefaultinfo Turns off usage of PTRACE_FAULTINFO, even if host supports it. To support PTRACE_FAULTINFO, the host needs to be patched using the current skas3 patch.
noprocmm Turns off usage of /proc/mm, even if host supports it. To support /proc/mm, the host needs to be patched using the current skas3 patch.
nosysemu Turns off syscall emulation patch for ptrace (SYSEMU) on. SYSEMU is a performance-patch introduced by Laurent Vivier. It changes behaviour of ptrace() and helps reducing host context switch rate. To make it working, you need a kernel patch for your host, too. See http://perso.wanadoo.fr/laurent.vivier/UML/ for further information.
—help Prints syntax information.
—version Prints the version number of the kernel.
—showconfig Prints the configuration used to build the kernel. To print all the options used to build the «linux» uml kernel and save them in «config_file» you can use
linux —showconfig > config_file
SEE ALSO¶
AUTHOR¶
User-mode Linux was written by Jeff Dike and others.
This manual page was written by Matt Zimmerman mdz@debian.org for the Debian GNU/Linux system, based on linux —help and the user-mode-linux website.
| Source file: | linux.uml.1.en.gz (from user-mode-linux 6.1um4+b3) |
| Source last updated: | 2023-05-18T09:00:38Z |
| Converted to HTML: | 2023-07-15T16:13:52Z |
Debian boot to single-user mode
I forgot my root password and am attempting to change it by booting into single-user mode, however when booting I get this screen: 
Then I press «e» to edit the boot configuration and I get this screen: 
However, in the tutorial I’m following it says I should navigate to the line that starts with «kernel», but as you can see, I dont have this line. So I tried changing «quiet» to «single» on the line that starts with «linux /boot/vmlinuz. » but this doesn’t boots the system into single-user mode. What line am I supposed to edit in order for this to work?
4 Answers 4
- Append init=/bin/bash to the end of the grub line which begins with linux (and ends with quiet ).
- Reset your password and reboot normally.
- Don’t forget it again.
- Consider installing sudo .
- Since this is apparently a virtual machine, you can mount its disk on another (working) virtual machine and manually remove the password from the /etc/shadow file. Or use kpartx to work with the virtual machine image file from the host or from another machine.
You probably don’t have a PATH . Try calling /usr/bin/passwd (or anything else) directly. Or just look around and see what you have available to you.
using /bin/bash as init won’t call any of the startup scripts to mount partitions, etc. either so if you have /usr in a separate partition you’ll need to mount it by hand. Also know that you won’t get the shutdown scripts either, when bash exits the kernel will immediately halt. Be sure to sync the drives first or changes may not be written.