Very Computer

Archive-Name: linux/faq/part1
Last-Modified: 21 Sep 1994

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This is the list of Frequently Asked Questions about Linux, the free Unix
for 386/486/586 [see Q1.1 `What is Linux ?' for more details].  It should
be read in conjunction with the HOWTO documents, which are available in

* ftp.funet.fi (128.214.6.100) : /pub/OS/Linux/doc/HOWTO
* tsx-11.mit.edu (18.172.1.2) : /pub/linux/docs/HOWTO
* sunsite.unc.edu (152.2.22.81) : /pub/Linux/docs/HOWTO

and mirror sites thereof -- see Q2.5 `Where can I get Linux material by
FTP ?'.  See Q2.1 `Where can I get the HOWTOs and other documentation ?'
for a list of the HOWTOs and more information.  The INFO-SHEET and
META-FAQ, found in the same place, also list other sources of Linux
information.

The Linux Documentation Project documentation is available on
sunsite.unc.edu in /pub/Linux/docs/LDP.  These documents (more are in
preparation) are invaluable to the newcomer or for use as a reference
work.

Please check out these documents and this FAQ, especially Q12.1 `You still
haven't answered my question !', before posting your question to the
newsgroup comp.os.linux.help.

See Q13.2 `Formats in which this FAQ is available' for details of where to
get the PostScript, Emacs Info, HTML (WWW) and plain ASCII versions of
this document.

You can skip to a particular question by searching for `Question n.n'.

Note that this posting has been split into two parts because of its size.

A new version of this document appears approximately monthly.  If this
copy is more than a month old it may be out of date.

===============================================================================

Index

 Section 1.  Introduction and General Information
 Q1.1        What is Linux ?
 Q1.2        What software does it support ?
 Q1.3        Does it run on my computer ?  What hardware is supported ?
 Q1.4        What ports to other processors are there ?
 Q1.5        How much hard disk space does Linux need ?
 Q1.6        Is Linux PD ?  Copyrighted ?

 Section 2.  Network sources and resources
 Q2.1        Where can I get the HOWTOs and other documentation ?
 Q2.2        Where should I look on the World Wide Web for Linux stuff ?
 Q2.3        What newsgroups are there for Linux ?
 Q2.4        How do I install Linux ?
 Q2.5        Where can I get Linux material by FTP ?
 Q2.6        I don't have FTP access.  Where do I get Linux ?
 Q2.7        I don't have Usenet access.  Where do I get information ?
 Q2.8        What's this mailing list thing at niksula.hut.fi ?
 Q2.9        Are the newsgroups archived anywhere ?

 Section 3.  Compatibility with other operating systems
 Q3.1        Can Linux coexist with DOS ?  OS/2 ?  386BSD ?  Minix ?
 Q3.2        How do I access files on my DOS partition or floppy ?
 Q3.3        Can I use my Stacked/DBLSPC/etc. DOS drive ?
 Q3.4        Can I access OS/2 HPFS partitions from Linux ?
 Q3.5        Can I access BSD FFS, SysV UFS, Mac, Amiga, etc filesystems ?
 Q3.6        Can I run Microsoft Windows programs under Linux ?
 Q3.7        How can I boot Linux from OS/2's Boot Manager ?
 Q3.8        How can I share a swap partition between Linux and MS Windows ?

 Section 4.  Linux's handling of filesystems, disks and drives
 Q4.1        How can I undelete files ?
 Q4.2        Is there a defragmenter for ext2fs etc. ?
 Q4.3        How do I format and create a filesystem on a floppy ?
 Q4.4        I get nasty messages about inodes, blocks, and the suchlike
 Q4.5        My swap area isn't working.
 Q4.6        How do I remove LILO so my system boots DOS again ?
 Q4.7        Why can't I use fdformat except as root ?
 Q4.8        Is there something like Stacker or Doublespace for Linux ?
 Q4.9        My ext2fs partitions are checked each time I reboot.
 Q4.10       I have a huge /proc/kcore !  Can I delete it ?
 Q4.11       My AHA1542C doesn't work with Linux.

 Section 5.  Porting, compiling and obtaining programs
 Q5.1        What is ld.so and where do I get it ?
 Q5.2        Has anyone ported / compiled / written XXX for Linux ?
 Q5.3        How do I port XXX to Linux ?
 Q5.4        Can I use code or a compiler compiled for a 486 on my 386 ?
 Q5.5        What does gcc -O6 do ?
 Q5.6        Where are <linux/*.h> and <asm/*.h> ?
 Q5.7        I get errors when I try to compile the kernel.
 Q5.8        How do I make a shared library ?
 Q5.9        How do I make my executables smaller ?

 Section 6.  Solutions to common miscellaneous problems
 Q6.1        Setuid scripts don't seem to work.
 Q6.2        Free memory as reported by free keeps shrinking.
 Q6.3        When I add more memory it slows to a crawl.
 Q6.4        Some programs (e.g. xdm) won't let me log in.
 Q6.5        Some programs let me log in with no password.
 Q6.6        My machine runs very slowly when I run GCC / X / ...
 Q6.7        I can only log in as root.
 Q6.8        My screen is all full of weird characters instead of letters.
 Q6.9        I have screwed up my system and can't log in to fix it.
 Q6.10       Emacs just dumps core.
 Q6.11       I've discovered a huge security hole in rm !
 Q6.12       lpr and/or lpd aren't working.

 Section 7.  How do I do this or find out that ... ?
 Q7.1        How can I get scrollback on text VC's ?
 Q7.2        How do I switch VC's ?  How do I enable them ?
 Q7.3        How do I set the timezone ?
 Q7.4        What version of Linux and what machine name am I using ?
 Q7.5        How can I enable or disable core dumps ?
 Q7.6        How do I upgrade/recompile my kernel ?
 Q7.7        Can I have more than 3 serial ports by sharing interrupts ?
 Q7.8        How do I make a bootable floppy ?
 Q7.9        How do I remap my keyboard to UK, French, etc. ?
 Q7.10       How do I get NUM LOCK to default to on ?

 Section 8.  Miscellaneous information and questions answered
 Q8.1        What is a .gz file ? And a .tgz ? And ... ?
 Q8.2        What does VFS stand for ?
 Q8.3        What is a BogoMip ?
 Q8.4        What is the Linux Journal and where can I get it ?
 Q8.5        How many people use Linux ?
 Q8.6        How should I pronounce Linux ?

 Section 9.  Frequently encountered error messages
 Q9.1        During linking I get Undefined symbol _mcount
 Q9.2        lp1 on fire
 Q9.3        INET: Warning: old style ioctl(IP_SET_DEV) called!
 Q9.4        ld: unrecognized option '-m486'
 Q9.5        GCC says Internal compiler error
 Q9.6        make says Error 139
 Q9.7        shell-init: permission denied when I log in.
 Q9.8        No utmp entry.  You must exec ... when I log in.
 Q9.9        Warning - bdflush not running
 Q9.10       Warning: obsolete routing request made.
 Q9.11       EXT2-fs: warning: mounting unchecked filesystem
 Q9.12       EXT2-fs warning: maximal count reached
 Q9.13       EXT2-fs warning: checktime reached
 Q9.14       df says Cannot read table of mounted filesystems
 Q9.15       fdisk says Partition X has different physical/logical ...
 Q9.16       fdisk: Partition 1 does not start on cylinder boundary
 Q9.17       fdisk says cannot use nnn sectors of this partition
 Q9.18       fdisk says partition n has an odd number of sectors
 Q9.19       mtools says cannot initialise drive XYZ

 Section 10. The X Window System
 Q10.1       Does Linux support X Windows ?
 Q10.2       Where can I get an Xconfig for my video card and monitor ?
 Q10.3       xterm logins show up strangely in who, finger
 Q10.4       I can't get X Windows to work right.

 Section 11. Questions applicable to very out-of-date software
 Q11.1       How can I have more than 16Mb of swap ?
 Q11.2       GCC sometimes uses huge amounts of virtual memory and thrashes
 Q11.3       My keyboard goes all funny after I switch VC's.

 Section 12. How to get further assistance
 Q12.1       You still haven't answered my question !
 Q12.2       What to put in a posting to comp.os.linux.help

 Section 13. Administrative information and acknowledgements
 Q13.1       Feedback is invited
 Q13.2       Formats in which this FAQ is available
 Q13.3       Authorship and acknowledgements
 Q13.4       Disclaimer and Copyright

===============================================================================

Section 1.  Introduction and General Information

 Q1.1        What is Linux ?
 Q1.2        What software does it support ?
 Q1.3        Does it run on my computer ?  What hardware is supported ?
 Q1.4        What ports to other processors are there ?
 Q1.5        How much hard disk space does Linux need ?
 Q1.6        Is Linux PD ?  Copyrighted ?

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Question 1.1.  What is Linux ?

Linux is a Unix clone written from scratch by Linus Torvalds with
assistance from a loosely-knit team of hackers across the Net.  It aims
towards POSIX compliance.

It has all the features you would expect in a modern fully-fledged Unix,
including true multitasking, virtual memory, shared libraries, demand
loading, shared copy-on-write executables, proper memory management and
TCP/IP networking.

It runs mainly on 386/486/586-based PCs, using the hardware facilities of
the 386 processor family (TSS segments et al) to implement these features.
Ports to other architectures are underway [Q1.4 `What ports to other
processors are there ?'].

See the Linux INFO-SHEET [Q2.1 `Where can I get the HOWTOs and other
documentation ?'] for more details.

The Linux kernel is distributed under the GNU General Public License - see
Q1.6 `Is Linux PD ?  Copyrighted ?' for more details.

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Question 1.2.  What software does it support ?

Linux has GCC, Emacs, X-Windows, all the standard Unix utilities, TCP/IP
(including SLIP and PPP) and all the hundreds of programs that people have
compiled or ported for it.

There is a DOS emulator [Q3.1 `Can Linux coexist with DOS ?  OS/2 ?
386BSD ?  Minix ?'] and work is progressing on a facilities to allow SVR4
ELF, SVR3.2 ...

read more »

Archive-Name: linux/faq/part2
Last-Modified: 21 Sep 1994

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(Continued from part 1, where you'll find the introduction and
 table of contents.)
===============================================================================

Section 6.  Solutions to common miscellaneous problems

 Q6.1        Setuid scripts don't seem to work.
 Q6.2        Free memory as reported by free keeps shrinking.
 Q6.3        When I add more memory it slows to a crawl.
 Q6.4        Some programs (e.g. xdm) won't let me log in.
 Q6.5        Some programs let me log in with no password.
 Q6.6        My machine runs very slowly when I run GCC / X / ...
 Q6.7        I can only log in as root.
 Q6.8        My screen is all full of weird characters instead of letters.
 Q6.9        I have screwed up my system and can't log in to fix it.
 Q6.10       Emacs just dumps core.
 Q6.11       I've discovered a huge security hole in rm !
 Q6.12       lpr and/or lpd aren't working.

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Question 6.1.  Setuid scripts don't seem to work.

That's right.  This feature has been deliberately disabled in the Linux
kernel because setuid scripts are almost always a security hole.  If you
want to know why read the FAQ for comp.unix.questions.

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Question 6.2.  Free memory as reported by free keeps shrinking.

The `free' figure printed by free doesn't include memory used as a disk
buffer cache - shown in the `buffers' column.  If you want to know how
much memory is really free add the `buffers' amount to `free'.

The disk buffer cache tends to grow soon after starting Linux up, as you
load more programs and use more files and the contents get cached.  It
will stabilise after a while.

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Question 6.3.  When I add more memory it slows to a crawl.

This is quite a common symptom of a failure to cache the additional
memory.  The exact problem depends on your motherboard.

Sometimes you have to enable caching of certain regions in your BIOS
setup.  Look in the CMOS setup and see if there is an option to cache the
new memory area which is currently switched off.  This is apparently most
common on a 486.

Sometimes the RAMs have to be in certain sockets to be cached.

Sometimes you have to set jumpers to enable the caching.

Some motherboards don't cache all the RAM if you have more RAM per amount
of cache than they expect.  Usually a full 256K cache will solve this
problem.

If in doubt, check your motherboard manual.  If you still can't fix it
because the documentation is inadequate you might like to post a message
giving *all* the details - make, model number, date code, etc. so that
other Linux users can avoid it.

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Question 6.4.  Some programs (e.g. xdm) won't let me log in.

You are probably using non-shadow-password programs but are using shadow
passwords.

If so, you have to get or compile a shadow password version of the
program(s) in question.  The shadow password suite can be found in
(amongst other places):
   tsx-11.mit.edu:/pub/linux/sources/usr.bin/shadow-*
This is the source code; you will probably find the binaries in
.../linux/binaries/usr.bin.

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Question 6.5.  Some programs let me log in with no password.

You probably have the same problem as in Q6.4 `Some programs (e.g. xdm)
won't let me log in.', with an added wrinkle:

If you are using shadow passords you should put an asterisk in the
password field of /etc/passwd for each account, so that if a program
doesn't know about the shadow passwords it won't think it's a passwordless
account and let anyone in.

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Question 6.6.  My machine runs very slowly when I run GCC / X / ...

You may not have any swap enabled.  You need to enable swapping to allow
Linux to page out bits of data programs aren't using at the moment to disk
to make more room for other programs and data.  If you don't Linux has to
keep data in memory and throw away in-memory copies of programs (which are
paged straight from the filesystem) and so less and less program is in
memory and everything runs very slowly.

See the Installation HOWTO and the Installation and Getting Started Guide
[Q2.1 `Where can I get the HOWTOs and other documentation ?'] for details
of how to set up a swap partition or swapfile; see also Q4.5 `My swap area
isn't working.'.

Alternatively you may have too little real memory.  If you have less RAM
than all the programs you're running at once use Linux will use your hard
disk instead and thrash horribly.  The solution in this case is to not run
so many things at once or to buy more memory.  You can also reclaim some
memory by compiling and using a kernel with less options configured.  See
Q7.6 `How do I upgrade/recompile my kernel ?'.

You can tell how much memory and/or swap you're using by using the free
command, or by typing
    cat /proc/meminfo

If your kernel is configured with a ramdisk this is probably wasted space
and will cause things to go slowly.  Use LILO or rdev to tell the kernel
not to allocate a ramdisk (see the LILO documentation or type man rdev).

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Question 6.7.  I can only log in as root.

You probably have some permission problems, or you have a file
/etc/nologin.

If the latter put rm -f /etc/nologin in your /etc/rc or /etc/rc.local.

Otherwise check the permissions on your shell, and any filenames which
appear in error messages, and also the directories containing these files
all the way back up the tree to the root directory.

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Question 6.8.  My screen is all full of weird characters instead of letters.

You probably sent some binary data to your screen by mistake.  Type echo
^V^[c (that's e c h o space control-V escape c return) to fix it.  Many
Linux distributions have a command reset that does this.

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Question 6.9.  I have screwed up my system and can't log in to fix it.

Reboot from an emergency floppy or floppy pair, for example the Slackware
boot- and root-disk pair (in the install subdirectory of the Slackware
mirrors) or the MCC installation boot floppy.  There are also two diy
rescue disk creation packages on sunsite.unc.edu in
/pub/Linux/system/Recovery.  These are better as they'll have your own
kernel on them, so that you don't run the risk of missing devices,
filesystems, etc.

Get to a shell prompt and mount your hard disk with something like
   mount -t ext2 /dev/hda1 /mnt

Then your filesystem is available under the directory /mnt and you can fix
the problem.  Remember to unmount your hard disk before rebooting (cd back
down to / first or it will say it's busy).

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Question 6.10.  Emacs just dumps core.

You probably have the X version of Emacs that comes with SLS.  It doesn't
work without the X libraries.  The solution is to install X Windows or get
a newer Emacs binary without any X Windows support.

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Question 6.11.  I've discovered a huge security hole in rm !

No you haven't.  You are obviously new to Unix and need to read a good
book on it to find out how things work.  Clue: ability to delete files
under Unix depends on permission to write the directory they are in.

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Question 6.12.  lpr and/or lpd aren't working.

Check the Printing HOWTO [Q2.1 `Where can I get the HOWTOs and other
documentation ?'].

===============================================================================

Section 7.  How do I do this or find out that ... ?

 Q7.1        How can I get scrollback on text VC's ?
 Q7.2        How do I switch VC's ?  How do I enable them ?
 Q7.3        How do I set the timezone ?
 Q7.4        What version of Linux and what machine name am I using ?
 Q7.5        How can I enable or disable core dumps ?
 Q7.6        How do I upgrade/recompile my kernel ?
 Q7.7        Can I have more than 3 serial ports by sharing interrupts ?
 Q7.8        How do I make a bootable floppy ?
 Q7.9        How do I remap my keyboard to UK, French, etc. ?
 Q7.10       How do I get NUM LOCK to default to on ?

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Question 7.1.  How can I get scrollback on text VC's ?

With the default US keymap you can use Shift with the PageUp and PageDown
keys (NB these must be the grey ones, not the ones on the numeric keypad
!).  With other keymaps check the maps in /usr/lib/keytables; you can
remap the scroll up and down keys to be whatever you like --- for example,
in order to remap them to keys that exist on an 84-key AT keyboard.

You can't increase the amount of scrollback, because of the way it is
implemented using the video memory to store the scrollback text, though
you may be able to get more scrollback in each VC by reducing the total
number of VC's --- see <linux/tty.h>.

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Question 7.2.  How do I switch VC's ?  How do I enable them ?

In text mode, press (Left) Alt-F1 to Alt-F12 to select tty1 to tty12.  To
switch out of X windows you must press Ctrl-Alt-F1 etc; Alt-F5 or whatever
will switch back.

Your kernel probably doesn't have all 12 compiled in; the default is 8.
This is controlled by NR_CONSOLES in linux/include/linux/tty.h.

If you want to use a VC for text ...

read more »