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Section 6. Solutions to common miscellaneous prob

2013-11-13 22:16:43  來源: Oracle 

  Q Setuid scripts dont seem to work
   Q Free memory as reported by free keeps shrinking
   Q When I add more memory it slows to a crawl
   Q Some programs (eg xdm) wont let me log in
   Q Some programs let me log in with no password
   Q My machine runs very slowly when I run GCC / X /
   Q I can only log in as root
   Q My screen is all full of weird characters instead of letters
   Q I have screwed up my system and cant log in to fix it
   Q Emacs just dumps core
   Q Ive discovered a huge security hole in rm !
   Q lpr and/or lpd arent working
  
  
  
  Question Setuid scripts dont seem to work
  
  Thats 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 compunixquestions
  
  
  
  Question Free memory as reported by free keeps shrinking
  
  The `free figure printed by free doesnt 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
  
  
  
  Question 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
  
  Sometimes the RAMs have to be in certain sockets to be cached
  
  Sometimes you have to set jumpers to enable the caching
  
  Some motherboards dont cache all the RAM if you have more RAM per amount
  of cache than they expect Usually a full K cache will solve this
  problem
  
  If in doubt check your motherboard manual If you still cant 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
  
  
  
  Question Some programs (eg xdm) wont let me log in
  
  You are probably using nonshadowpassword 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):
   tsxmitedu:/pub/linux/sources/usrbin/shadow*
  This is the source code; you will probably find the binaries in
  /linux/binaries/usrbin
  
  
  
  Question Some programs let me log in with no password
  
  You probably have the same problem as in Q `Some programs (eg xdm)
  wont 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
  doesnt know about the shadow passwords it wont think its a passwordless
  account and let anyone in
  
  
  
  Question 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 arent using at the moment to disk
  to make more room for other programs and data If you dont Linux has to
  keep data in memory and throw away inmemory 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
  [Q `Where can I get the HOWTOs and other documentation ?] for details
  of how to set up a swap partition or swapfile; see also Q `My swap area
  isnt working
  
  Alternatively you may have too little real memory If you have less RAM
  than all the programs youre 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
  Q `How do I upgrade/recompile my kernel ?
  
  You can tell how much memory and/or swap youre 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)
  
  
  
  Question 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/rclocal
  
  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
  
  
  
  Question 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 (thats e c h o space controlV escape c return) to fix it Many
  Linux distributions have a command reset that does this
  
  
  
  Question I have screwed up my system and cant log in to fix it
  
  Reboot from an emergency floppy or floppy pair for example the Slackware
  boot and rootdisk 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 sunsiteuncedu in
  /pub/Linux/system/Recovery These are better as theyll have your own
  kernel on them so that you dont run the risk of missing devices
  filesystems etc
  
  Get to a shell prompt and mount your hard disk with something like
   mount t ext /dev/hda /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 its busy)
  
  
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