知识大全 Section 6. Solutions to common miscellaneous prob

Posted 2022-07-15 文字

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　　Q Setuid scripts don t 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 (e g xdm) won t 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 can t log in to fix it 　　 Q Emacs just dumps core 　　 Q I ve discovered a huge security hole in rm !　　 Q lpr and/or lpd aren t working 　　　　　　　　Question 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 p unix questions 　　　　　　　　Question 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 　　　　　　　　Question When I add more memory it slows to a crawl 　　　　This is quite a mon 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　　mon 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 don t 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 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 　　　　　　　　Question 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 pile a shadow password version of the　　program(s) in question The shadow password suite can be found in　　(amongst other places):　　 tsx mit edu:/pub/linux/sources/usr bin/shadow *　　This is the source code; you will probably find the binaries in　　 /linux/binaries/usr bin 　　　　　　　　Question Some programs let me log in with no password 　　　　You probably have the same problem as in Q `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 　　　　　　　　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 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　　[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　　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 piling and using a kernel with less options configured See　　Q `How do I upgrade/repile my kernel ? 　　　　You can tell how much memory and/or swap you re using by using the free　　mand 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/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 　　　　　　　　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 (that s e c h o space control V escape c return) to fix it Many　　Linux distributions have a mand reset that does this 　　　　　　　　Question 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 o 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 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 it s busy) 　　　　 cha138/Article/program/Oracle/201311/18664