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<nowiki> ____________________________</nowiki> <nowiki> / \</nowiki> <nowiki> ( Krissy's Question and Answer )</nowiki> <nowiki> \____________________________/</nowiki> <nowiki></nowiki> <nowiki></nowiki> <nowiki>Q&A CORE FILES (finding core files everywhere on the file system)</nowiki> <nowiki>----------</nowiki> <nowiki>Q: what are those core files?</nowiki> <nowiki>A: do "file core" and it'll tell you who made the core file.</nowiki> <nowiki>Q: what is causing them, improper shutdown maybe?</nowiki> <nowiki>A: more like a dodgy/corrupt library or something. when a *nix </nowiki> <nowiki> program crashes, it creates a core file that someone smart can use</nowiki> <nowiki> to help debug the program or determine why it crashed.</nowiki> <nowiki>Q: is it always the same program that is dumping core files?</nowiki> <nowiki>A: I would say that this is a glibc issue. you could do a</nowiki> <nowiki> 'gdb /usr/bin/who core' on that core file.</nowiki> <nowiki></nowiki> <nowiki>Q&A UPGRADED MEMORY (upgraded my ram but linux can't see it)</nowiki> <nowiki>----------</nowiki> <nowiki>Q: how do I get linux to see all of my ram, I just upgraded?</nowiki> <nowiki>A: edit /etc/lilo.conf add: 'boot: linux mem=127M' (always 1</nowiki> <nowiki> mb less than actual system ram)</nowiki> <nowiki></nowiki> <nowiki>Q&A BASH SHELL QUESTIONS</nowiki> <nowiki>----------</nowiki> <nowiki>Q: how do I filter my log file when viewing it with tail -f?</nowiki> <nowiki>A: filter out individual lines with grep. parsing within the</nowiki> <nowiki> line is not possible using sed when using tail -f because</nowiki> <nowiki> sed does not seem to flush. Instead use gawk. Here is an</nowiki> <nowiki> ex: tail -f access_log | gawk '{sub(/GET/,"get");print}'</nowiki> <nowiki>Q: how to search for a file or pattern without locate?</nowiki> <nowiki>A: the find command can be used. here are examples:</nowiki> <nowiki> find ./ -name filename (locate filename in or below the</nowiki> <nowiki> current directory path)</nowiki> <nowiki> find / -name 'filename' 2>/dev/null (locate filename </nowiki> <nowiki> anywhere up from root filesystem)</nowiki> <nowiki> find ./ -iname 'filen*' (locate all files begin with</nowiki> <nowiki> filen and ignore case)</nowiki> <nowiki>Q: this filename begins with a dash "-" and I don't know how</nowiki> <nowiki> to delete it, rm just returns errors even when I backslash.</nowiki> <nowiki>A: rm thinks the dash indicates that you are passing a command</nowiki> <nowiki> line argument. adding two dashes behind the command tells</nowiki> <nowiki> it there will be no more arguments. To create a file and</nowiki> <nowiki> delete it when the first character is a dash:</nowiki> <nowiki> ex: touch -- -filename</nowiki> <nowiki> ex: rm -- -filename</nowiki> <nowiki></nowiki> <nowiki>Q&A SYSTEM VERSION INFORMATION</nowiki> <nowiki>----------</nowiki> [[Determining Your Linux Version]] <nowiki>Q: how can I tell what linux kernel version I have?</nowiki> <nowiki>A: type 'uname -s -r'</nowiki> <nowiki>Q: how can I tell what gcc version I have?</nowiki> <nowiki>A: type 'gcc --version'</nowiki> <nowiki>Q: how can I tell what glibc version I have?</nowiki> <nowiki>A: type '/lib/libc.so.6'</nowiki> <nowiki>Q: how can I tell what vesion of xwindows I have?</nowiki> <nowiki>A: type 'XFree86 -version' or 'xdpyinfo'</nowiki> <nowiki>Q: how can I tell what Linux Distribution I have?</nowiki> <nowiki>A: sorry, there is no one super command to accomplish this. </nowiki> <nowiki> Instead you will need to make some observations.</nowiki> <nowiki> Use 'dmesg' to see if system displayed distro during boot.</nowiki> <nowiki> Check for presence of certail signature distro files,</nowiki> <nowiki> Redhat creates '/etc/redhat-release'</nowiki> <nowiki> SuSE creates '/etc/SuSE-release'</nowiki> <nowiki> Debian creates '/etc/debian_version'</nowiki> <nowiki> You may also check the issue or issue.net file</nowiki> <nowiki> type 'cat /etc/issue'</nowiki> <nowiki></nowiki> <nowiki>Q&A SYSTEM AND TERMONOLOGY</nowiki> <nowiki>----------</nowiki> <nowiki>Q: what is pam.d and pam authentication for linux?</nowiki> <nowiki>A: Pluggable Authentication Modules, or PAM handles authentication</nowiki> <nowiki> for services and is used by login and su. On RH each service or </nowiki> <nowiki> application that uses pam has a configuration file in /etc/pam.d</nowiki> <nowiki> in short, pam is an authentication api</nowiki> <nowiki>Q: what are the advantages of using pam?</nowiki> <nowiki>A: allows every program to use a common API for authentication. </nowiki> <nowiki> otherwise, if a new auth mechanism is introducted, each </nowiki> <nowiki> application would have to be updated to support the new mechanism</nowiki> <nowiki>Q: what are tcp wrappers?</nowiki> <nowiki>A: access control facility for internet services or tcpd which looks </nowiki> <nowiki> at hosts.allow and hosts.deny when connection attempts handshake</nowiki> <nowiki>Q: how do you determine what services use hosts.deny and hosts.allow?</nowiki> <nowiki>A: inetd or xinetd.d servises that use tcp wrappers. remote hosts </nowiki> <nowiki> first make a handshake with tcpd, tcpd looks to the two files.</nowiki> <nowiki>Q: some services that use hosts.allow/deny arn't in xinet.d. why?</nowiki> <nowiki>A: ssh is not an xinet.d service even though it still uses tcp </nowiki> <nowiki> wrappers. there is an entry for sshd in /etc/init.d</nowiki> <nowiki> on a RH system sshd is configured to use tcp wrappers. if you </nowiki> <nowiki> build your own secure shell then you want to use tcp wrappers:</nowiki> <nowiki> ./configure --with-libwrap=/usr/local/lib/libwrap.a</nowiki> <nowiki></nowiki> <nowiki>Q&A SYSTEM START AND SYSTEM-V</nowiki> <nowiki>----------</nowiki> <nowiki>Q: how does the RH System-V boot system work and how's it configured?</nowiki> <nowiki>A: the base directory /etc/init.d contains a start/stop script for </nowiki> <nowiki> each daemon process, and symbolic links in the rc<N>.d subdirs </nowiki> <nowiki> control which scripts are run when entering or leaving a runlevel. </nowiki> <nowiki> The links point back into the start/stop script in the parent dir, </nowiki> <nowiki> using a "S" prefix for the starting link, and "K" for stopping. </nowiki> <nowiki> The numeric part of the link name determines the order they start.</nowiki> <nowiki></nowiki> <nowiki>Q&A FILE AND DIRECTORY PERMISSIONS</nowiki> <nowiki>----------</nowiki> <nowiki>Q: what are all the file permission letters and what does each one represent?</nowiki> <nowiki>A: letters `rwxXstugo' represent (r)=read (w)=write </nowiki> <nowiki> (x)=execute file or access directory (t)=sticky</nowiki> <nowiki> (X)=execute only if is directory or has x for someone else</nowiki> <nowiki> (s)=set user/group id on execution (setuid bit)</nowiki> <nowiki> (u)=permissions granted to user who owns file (g)="" in file group</nowiki> <nowiki> (o)=permissions for users not owning file or in group.</nowiki> <nowiki>Q: what is the setuid bit (s) and what does it do?</nowiki> <nowiki>A: setuid bit is only in the execute field. the function when used on files</nowiki> <nowiki> is different when used on directories. using setuid on an executable means</nowiki> <nowiki> when the file is executed by anyone, it will run as though you executed it</nowiki> <nowiki> (or run as the user owning the file when it's setuid)</nowiki> <nowiki>Q: how do you set the setuid bit and getgid bit for a file or directory?</nowiki> <nowiki>A: the command syntax, chmod u+s and chmod g+s or using the numeric file</nowiki> <nowiki> permissions, chmod 4777 and chmod 2777 (make the 777 whatever you want)</nowiki> <nowiki> also, in combinations like chmod 6777 setuid/setgid and read/write/execute</nowiki> <nowiki></nowiki> <nowiki>Q&A REMOTE ACCESS AND TERMINALS</nowiki> <nowiki>----------</nowiki> <nowiki>Q: what remote access connection service should I use, telnet, rlogin, ssh?</nowiki> <nowiki>A: ssh2</nowiki> <nowiki>Q: is there an alternative to putty?</nowiki> <nowiki>A: yes. Secure CRT is a commercial alternative and has more features.</nowiki> <nowiki>Q: how do I enable compression in SecureCRT for my ssh2 connection?</nowiki> <nowiki>A: in the connections dialog click the advanced button to the right of the</nowiki> <nowiki> connection hostname field. The compression may be set in teh general</nowiki> <nowiki> tab of the advanced dialog.</nowiki> <nowiki></nowiki> <nowiki></nowiki> <nowiki>Questions / Comments to: krissyj at robotz dot com</nowiki> <nowiki> </nowiki> {{:Template:Archived Entry}} [[Category:Legacy Notes]] [[Category:Computer_Technology]] [[Category:Linux]]

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