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To access the contents, click the chapter and section titles.
Complete Idiot's Guide to Linux
Finding out How Much Disk Files Consume: duThe disk usage program, du, allows you to get a listing of how much space a directory eats up, given in 1K increments. By default, it will print an entry for each directory it finds, like this: [alberto@digital alberto]$ du 14 ./.seyon 3 ./lg/lg_layouts 1 ./lg/.lgDESKTOP 1 ./lg/lg3_hosts 15 ./lg 40 ./.kde/share/config 1 ./.kde/share/apps/kfm/tmp 1 ./.kde/share/apps/kfm/bookmarks 6 ./.kde/share/apps/kfm 4 ./.kde/share/apps/kdehelp 2 ./.kde/share/apps/knotes/notes 1 ./.kde/share/apps/knotes/xyalarms 5 ./.kde/share/apps/knotes 1 ./.kde/share/apps/kppp/Rules To summarize output, specify the -s option, as in the following: [alberto@digital alberto]$ du -s 23670 . To specify specific directories or files to list, provide their names as arguments, like this: [root@digital /home]# du -s * 23670 alberto 32 cool 32 digital 35 flower 583 ftp 1582 httpd 1 public 1 samba 1 test_project In this example, all home directories are summarized. Finding the Amount of Free Disk Space: dfTo find the amount of disk space to devices available in your system, use the df (disk free) command, as shown in the following: [root@digital /home]# df Filesystem 1024-blocks Used Available Capacity Mounted on /dev/hda1 686892 606189 45223 93% / The command produces a nice table specifying how much space is available. Numbers are expressed in kilobytes. In UNIX/Linux, just because theres free space doesnt mean that you can create files. If the file systems inode table fills up (unlikely, but possible if a disk holds a great deal of tiny files), your system would be unable to create additional files. To see how you are doing on inodes, provide the -i option to df: [root@digital /home]# df -i Filesystem Inodes IUsed IFree %IUsed Mounted on /dev/hda1 177480 34971 142509 20% / If you compare the regular df output, youll see that under normal circumstances, there are plenty of inodes left. On my disk, I have used 93% of my disk, yet only 20% of the inodes. Log FilesMany of the programs that run in the background, Web server, email, FTP, and so on generate logs for errors or just as a record of someone accessing it. This type of information is recorded, for example, every time a user logs in or out of the system. Monitoring Logins: lastLinux keeps very good track of users and their logins. This information is particularly useful when you are in a networked environment, and as a security precaution, you check to make sure that no weird traffic is going on in your machine. By default, Linux is set up to keep track of logins and logouts. You can browse the login record using the last command. To filter output to a specific user, provide the username as an argument to last: [alberto@digital log]$ last alberto alberto ttyp0 192.168.0.3 Fri Oct 2 18:32 still logged in alberto ttyp0 192.168.0.3 Fri Oct 2 18:29 - 18:32 alberto tty2 Fri Oct 2 15:20 - 17:01 (01:40) alberto ttyp1 192.168.0.3 Fri Oct 2 14:55 - down (03:32) alberto ftp 192.168.0.3 Fri Oct 2 13:41 - 13:42 (00:00) alberto ftp 192.168.0.3 Fri Oct 2 13:12 - 13:28 (00:16) alberto tty1 Fri Oct 2 13:02 - down (05:25) alberto tty1 Wed Sep 30 17:41 - down (00:18) alberto tty1 Tue Sep 29 11:10 - down (00:10) alberto tty1 Mon Sep 28 17:36 - down (00:47) The last command prints the username, the terminal used to access the system, where the user came from (IP address) if the login was remote, and the date and duration of the session. If the log file /var/log/wtmp doesnt exist in your system, the system will not keep track of login information. To enable (or disable) this feature, just create or delete this file. Monitoring Bad Logins: lastbThe lastb command keeps track of bad (unsuccessful) logins. To enable bad login accounting, as root create the file /var/log/btmp. You can do this using the touch command (touch /var/log/btmp). To review bad logins, use the lastb command. Unfortunately, Caldera OpenLinux doesnt currently support lastb use. If an account has an unusual number of bad logins, it is possible that the account is under attack by someone. Such accounts should be disabled and the user owning the account should be notified. Disabling an Account The easiest way to disable an account is to put an asterisk (*) before the encrypted password in the /etc/passwd file. (The password is the second field in /etc/passwd.) Fields are separated by colons (:), like this: me:*Ms.7kvaAYyHbU:500:100:Me:/home/me:/bin/sh If you are using shadow passwords, the easiest way to disable an account is to use usermod and expire it with a date in the past: usermod -e MM/DD/YY login [root@digital alberto]# usermod -e 09/01/98 me (Usermod is introduced in Chapter 18, Users, Groups, and Passwords.)
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