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Sudo

Sudo. Yi-Hsiang Lin yslin@cis.nctu.edu.tw 2002/5/21 @ CISCC. OUTLINE. Introduction Related files of command “sudo” The options of command “sudo” Examples of command “sudo” The file formats of “sudoers” grammar, aliases Examples of file “sudoers” entries. Introduction.

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Sudo

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  1. Sudo Yi-Hsiang Lin yslin@cis.nctu.edu.tw 2002/5/21 @ CISCC

  2. OUTLINE • Introduction • Related files of command “sudo” • The options of command “sudo” • Examples of command “sudo” • The file formats of “sudoers”grammar, aliases • Examples of file “sudoers” entries

  3. Introduction • Sudo allows a permitted user to execute a command as the superuser or another user • Sudo use user’s password • When authenticated, a timestamp is used. User can use sudo without a password for 5 minutes • log both successful and unsuccessful

  4. Related files of sudo • sudo : under /usr/bin or /usr/local/bin- execute a command as another user • sudoers: under /etc or /usr/local/etc- list of which users may execute what • visudo: under /usr/sbin or /usr/local/sbin- edit the sudoers file • /var/run/sudo:Directory containing timestamps

  5. The options of sudo(1/2) • -V: Version • -l: list allowed commands • -L: list defaults – Defaults parameters • -h: help • -v: validate – update timestamp • -k: kill – invalidate timestamp • -K: sure kill – remove timestamp entirely

  6. The options of sudo(2/2) • -b: background • -p: prompt – override the default prompt • -c: class • -a: authentication • -u: user – username or #uid • -s: shell • -H: HOME • -S: stdin

  7. Examples of sudo • Listing of an unreadable directory% sudo ls /usr/local/protected • List home dir. of ~zjm which is not exported as root:% sudo -u zjm ls ~zjm • Edit the index.html file as user www% sudo -u www vi ~www/htdocs/index.html • Shutdown a machine% sudo shutdown -r +15 "quick reboot“ • runs the commands in a subshell to make the cd and file redirection work% sudo sh -c "cd /home ; du -s * | sort -rn > USAGE"

  8. The file formats of “sudoers” – grammar • GRAMMAR:Use Extended Backus-Naur Form (EBNF) symbol ::= definition | alternate1 | alternate2 ...? : Means that the preceding symbol is optional. It may appear once or not at all* : Means that the preceding symbol may appear zero or more times.+ : Means that the preceding symbol may appear one or more times.

  9. The file formats of “sudoers” – aliases • four kinds of aliases:User_Alias, Runas_Alias, Host_Alias and Cmnd_Alias. • Alias ::= 'User_Alias' = User_Alias (':' User_Alias)* |'Runas_Alias' = Runas_Alias (':' Runas_Alias)* |'Host_Alias' = Host_Alias (':' Host_Alias)* |'Cmnd_Alias' = Cmnd_Alias (':' Cmnd_Alias)* • User_Alias ::= NAME '=' User_List • NAME ::= [A-Z]([A-Z][0-9]_)* • Please man sudoers for details

  10. Examples of file “sudoers” entries(1) # User alias specification User_Alias FULLTIMERS = millert, mikef, dowdy User_Alias PARTTIMERS = bostley, jwfox, crawl User_Alias WEBMASTERS = will, wendy, wim # Runas alias specification Runas_Alias OP = root, operator Runas_Alias DB = oracle, sybase # Host alias specification Host_Alias SPARC = bigtime, eclipse, moet, anchor :\ SGI = grolsch, dandelion, black :\ ALPHA = widget, thalamus, foobar :\ HPPA = boa, nag, python Host_Alias CUNETS = 128.138.0.0/255.255.0.0 Host_Alias CSNETS = 128.138.243.0, 128.138.204.0/24, \ 128.138.242.0 Host_Alias SERVERS = master, mail, www, ns Host_Alias CDROM = orion, perseus, hercules

  11. Examples of file “sudoers” entries(2) # Cmnd alias specification Cmnd_Alias DUMPS = /usr/bin/mt, /usr/sbin/dump, \ /usr/sbin/rdump,\ /usr/sbin/restore, /usr/sbin/rrestore Cmnd_Alias KILL = /usr/bin/kill Cmnd_Alias PRINTING = /usr/sbin/lpc, /usr/bin/lprm Cmnd_Alias SHUTDOWN = /usr/sbin/shutdown Cmnd_Alias HALT = /usr/sbin/halt, /usr/sbin/fasthalt Cmnd_Alias REBOOT = /usr/sbin/reboot, /usr/sbin/fastboot Cmnd_Alias SHELLS = /usr/bin/sh, /usr/bin/csh, /usr/bin/ksh, \ /usr/local/bin/tcsh, /usr/bin/rsh, \ /usr/local/bin/zsh Cmnd_Alias SU = /usr/bin/su

  12. Examples of file “sudoers” entries(3) # Override built in defaults Defaults syslog=auth Defaults:FULLTIMERS !lecture Defaults:millert !authenticate Defaults@SERVERS log_year, logfile=/var/log/sudo.log root ALL = (ALL) ALL %wheel ALL = (ALL) ALL FULLTIMERS ALL = NOPASSWD: ALL PARTTIMERS ALL = ALL jack CSNETS = ALL lisa CUNETS = ALL operator ALL = DUMPS, KILL, PRINTING, SHUTDOWN, HALT, REBOOT, /usr/oper/bin/

  13. Examples of file “sudoers” entries(4) joe ALL = /usr/bin/su operator pete HPPA = /usr/bin/passwd [A-z]*, !/usr/bin/passwd root bob SPARC = (OP) ALL : SGI = (OP) ALL jim +biglab = ALL +secretaries ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuser fred ALL = (DB) NOPASSWD: ALL john ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root* jen ALL, !SERVERS = ALL jill SERVERS = /usr/bin/, !SU, !SHELLS steve CSNETS = (operator) /usr/local/op_commands/ matt valkyrie = KILL WEBMASTERS www = (www) ALL, (root) /usr/bin/su www ALL CDROM = NOPASSWD: /sbin/umount /CDROM,\ /sbin/mount -o nosuid\,nodev /dev/cd0a /CDROM bill ALL = ALL, !SU, !SHELLS

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