How do I drop to shell from rescue CD???
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From: The Natural Philosopher on 19 May 2010 17:02 Ohhhh maaan wrote: > Gernot Fink wrote: > >> In article <i%WIn.16205$TL5.12659(a)newsfe24.iad>, >> Ohhhh maaan <nobodyhere(a)example.com> writes: >>> Hans-Peter Diettrich wrote: >>> >>>> Ohhhh maaan schrieb: >>>> >>>>> I have a kernel panic and need to fix a typo. I don't have the >>>>> install disks, and I just want to use the CD to access the shell >>>>> prompt so I can run the commands need. I can't get to the grub boot >>>>> loader screen. >>>> Can you still boot any live-CD, and apply your corrections from >>>> there? >>>> >>>> DoDi >>> I may be able to, I will check. I suppose, in the meantime, that the >>> rescue CD is intended for a specific purpose then and it's not >>> something you can drop into shell from (at least without physical >>> console access or going through some rescue mode steps)? >> try PLD-rescuecd(50MB) or systemrescuecd(200MB). Both are gerneral >> rich featured shellbased RescueCDs. >> > > I appreciate the suggestion, but the data center only has on hand what > they have and I didn't want to make a big deal about it with them, and > I don't need anything beyond the very basic. I was just wondering if > someone can use a rescue CD in the same manner you'd be able to use a > Live CD. I didn't want to have to ask them to swap it out (if they even > have it on hand) if I could have just dropped into shell from the > rescue CD. I suppose this answers my question though, there is no way > to do this it seems (or no one seems to know)... unless there's > something unique happening with this file system, I suppose. > Regardless, I've made a mental note about the shell based rescue CD's, > which could come in handy (I can't stand remote GUI interfaces over KVM > anyway). another possibility is to slap another disk in the primary, install to that, mount the original and fix it.
From: Keith Keller on 19 May 2010 17:03 On 2010-05-19, Ohhhh maaan <nobodyhere(a)example.com> wrote: > > Yes, but the issue is the installed kernel. I need to just run grub for > it. I don't understand what this is supposed to mean. Is grub installed into the MBR? Does grub start after the BIOS is done? Is the change you need to make simply fixing the grub configuration? It'd be really helpful if you explained in more detail the problem you need to fix. > I would certainly consider this, if this were an option at the DC. It > might be, but I suppose this is my question; Can you just do this from > a rescue CD? I used to do it in RH 4, etc. a long time ago, so does > that option/method not exist now? So, I need a live CD, not a rescue > CD? There's no technical difference between a live CD, a rescue CD, and an install CD: they all boot some sort of linux kernel, and start up some programs once an init takes over. The difference is mainly cosmetic: typically a ''live'' CD is close to what a ''normal'' user would expect from booting a full distribution from hard disk (e.g., with full networking, X, possibly even KDE or GNOME). A ''rescue'' CD often comes with extra utilities for testing or recovering from drastic error scenarios. And an ''install'' CD runs the installer program that the distro maintainers wrote (and sometimes makes it slightly more difficult to deviate from the install process). But, as others have mentioned, in most cases access to a shell is always there. I know that the CentOS installer does allow you to switch to a different virtual console with Ctrl-Alt-Fn (n=1,2,3,4, possibly 5 and 6?). Since the remote KVM is in the middle this switching is obviously more complicated. It'll definitely be worth investigating how to pass these sequences down the channel, so that if you have difficulty in the future you'll be able to switch VCs. Another boot CD will have different utilities available for you; the advantage of using the CentOS CD is that you know the versions of its software will be very close to your installed distro (and should be able to support anything more exotic you did, such as LVM or unusual filesystems). But if you know what your environment is like, *any* boot CD that supports it will work fine to manipulate the filesystems. In particular, if you need to modify the grub configuration, all you really need is filesystem support (including LVM if you used that) and an editor. Google "linux rescue cd" for many different options. --keith -- kkeller-usenet(a)wombat.san-francisco.ca.us (try just my userid to email me) AOLSFAQ=http://www.therockgarden.ca/aolsfaq.txt see X- headers for PGP signature information
From: Keith Keller on 19 May 2010 17:09 On 2010-05-19, Ohhhh maaan <nobodyhere(a)example.com> wrote: > > I appreciate the suggestion, but the data center only has on hand what > they have and I didn't want to make a big deal about it with them, and > I don't need anything beyond the very basic. I was just wondering if > someone can use a rescue CD in the same manner you'd be able to use a > Live CD. I didn't want to have to ask them to swap it out (if they even > have it on hand) if I could have just dropped into shell from the > rescue CD. I suppose this answers my question though, there is no way > to do this it seems (or no one seems to know) People do know. As I and others have mentioned, the CentOS install CD supports multiple virtual consoles, but you need to be able to pass through Ctrl-Alt-Fn (or in some cases just Alt-Fn) to the console. > ... unless there's > something unique happening with this file system, I suppose. It almost certainly has nothing to do with the filesystem. > Regardless, I've made a mental note about the shell based rescue CD's, > which could come in handy (I can't stand remote GUI interfaces over KVM > anyway). Agreed. You can try out the various non-GUI CDs locally (preferably on hardware that comes close to what you have at your remote data center), pick the one you like, and send that to the DC ops people. --keith -- kkeller-usenet(a)wombat.san-francisco.ca.us (try just my userid to email me) AOLSFAQ=http://www.therockgarden.ca/aolsfaq.txt see X- headers for PGP signature information
From: unruh on 19 May 2010 18:22 On 2010-05-19, Ohhhh maaan <nobodyhere(a)example.com> wrote: > unruh wrote: > >> On 2010-05-19, Ohhhh maaan <nobodyhere(a)example.com> wrote: >>> Keith Keller wrote: >>> >>>> ["Followup-To:" header set to comp.os.linux.misc.] >>>> >>>> On 2010-05-19, Ohhhh maaan <nobodyhere(a)example.com> wrote: >>>>> >>>>> I've used Linux years ago and I think I recall you could just type >>>>> linux single or linux emergency at the boot CD, but nothing works >>>>> with this new CentOS 5.x rescue CD. I'm stuck at "boot:" and >>>>> nothing I try just drops/boots me into a shell prompt. Please, >>>>> help! :) >>>> >>>> Close: it's linux rescue, not emergency: >>>> >>>> >>> > http://www.centos.org/docs/5/html/Installation_Guide-en-US/s1-rescuemode-boot.html >>>> >>>> But I believe the onscreen text tells you to hit F5 for help and >>>> other boot options, so you should look for that next time. See e.g. >>>> >>>> http://www.go2linux.org/pics/centos-base/Screenshot.png >>>> >>>> Hitting F5 gives you more information on booting the CD in rescue >>>> mode. >>>> >>>> --keith >>>> >>> >>> Yes, I know what it says. I did that already, and it just goes to the >>> same install screen. Doesn't matter if I type linux, linux text, >>> linux rescue, or just hit enter, or try linux single, linux >>> emergency, or anything else, it _always_ goes to the text menus and >>> doesn't allow me to break out of it or drop to a shell prompt, or >>> anything else. It just >>> wants the install disk images. In fact, the link you've provided >>> says it all: >>> >>> "Once you have booted using one of the described methods, add the >>> keyword rescue as a kernel parameter. For example, for an x86 system, >>> type the following command at the installation boot prompt: >>> >>> >>> linux rescue >>> >>> >>> >>> You are prompted to answer a few basic questions, including which >>> language to use. It also prompts you to select where a valid rescue >>> image is located. Select from Local CD-ROM, Hard Drive, NFS image, >>> FTP, or HTTP. The location selected must contain a valid installation >>> tree " >>> >>> It simply does not allow me to skip or select any options that allow >>> me to even get to the point where I can get shell access. I >>> definitely recall that the boot CD's allowed a person to jump right >>> into a shell if they wanted, even without using the installed >>> bootloader, and I can't find any information to show where someone >>> can just boot from the CD's kernel and drop into a shell and run >>> commands (it always wants the install images). >> >> Uh, the shell runs on top of the kernel. > > Yes, I know. > >> It MUST load a kernel to run >> the shell, > > Yes, that is the point to the boot CD. No The boot cd simply loads an braindead little program which then loads the kernel. It itself does not load the kernel. (Well it depends on which "boot CD" you have) > >> so tell it where to get tthe kernel so you can run the >> shell. > > It will not boot another kernel, thus I'm locked into the rescue mode > steps. This is the problem. Tell us what you have as what you call a "boot cd" > > So, do you know how to drop into shell after the rescue CD's kernel is > loaded and not go through the rescue steps that want the CentOS images, > so I can just drop into shell? I do not use redhat or centos, so cannot swear, but I suspect that it is not loading a kernel, but simply a little program that asks you questions so it knows which kernel and which options to that kernel to use. > >
From: unruh on 19 May 2010 18:29
On 2010-05-19, Ohhhh maaan <nobodyhere(a)example.com> wrote: > unruh wrote: > >> On 2010-05-19, Ohhhh maaan <nobodyhere(a)example.com> wrote: >>> I have a kernel panic and need to fix a typo. I don't have the >>> install disks, and I just want to use the CD to access the shell >>> prompt so I can run the commands need. I can't get to the grub boot >>> loader screen. >>> >>> Anyway, I run this and it asks for linux or linux text, and no matter >>> what I do, I can't just have it load the kernel image from the rescue >>> CD and drop into shell. It always wants to install and asks for the >>> images. How in the world can someone just drop into a shell prompt? >>> >>> I've used Linux years ago and I think I recall you could just type >>> linux single or linux emergency at the boot CD, but nothing works >>> with this new CentOS 5.x rescue CD. I'm stuck at "boot:" and nothing >>> I try just drops/boots me into a shell prompt. Please, help! :) >> >> Did you try typing "rescue" when it is stuck at "boot:"? > > Yes, of course. And, it went into rescue, which is not what I want. Or, > is this entire issue about some issue with the file system where it > should otherwise BE dropping into shell? This is what I'm trying to > figure out. What? You tell us you want to go into rescue and then when it goes into rescue you say "that is not what I want" What do you want? Go into rescue, mount the partitions, fix them and reboot |