Linux+ Chapter7

Front 1

Group membership is controlled through the

Back 1

Group membership is controlled through the /etc/group file.
contains a list of groups and the members belonging to each group

Front 2

Where the user’s primary group is set

Back 2

is set in the user’s configuration in /etc/passwd (the file
that defines accounts)

Front 3

To run programs or create files with a group other than the primary one, however, the user must run the __________ cmd to switch the current group membership

Back 3

newgrp project2

Front 4

IDs range for system uses?

Back 4

system 0 - 99

0 is root

Front 5

Adding users can be accomplished through the _____ utility

Back 5

useradd [-c comment] [-d home-dir] [-e expire-date] [-f inactive-days] [-g default-group] [-G group[,...]] [-m [-k skeleton-dir] | -M] [-p password] [-s shell] [-u UID [-o]] [-r] [-n] username

Front 6

When using useradd <username> without any parameter the default values are applied
Where are the default values for the system stored

Back 6

/etc/login.defs

Front 7

useradd parameter
comment
home director
account expiration

Back 7

comment
-c comment

home directory
-d home-dir
def is /home/username

account expiration
-e expire-date

Front 8

useradd parameter
inactive days
default group

Back 8

inactive days
-f inactive day
-1 to disable account expiration

default group
-g default-group
name or GID of the default user group

Front 9

useradd parameter
additional groups
home dire option
no home dire creation

Back 9

additional groups
-G grpup[,...]

home dir option
-m swicht automatically create the user home dir

no home dire creation
-M

Front 10

useradd parameter
encrypted password specification
default shell
UID

Back 10

encrypted password specification
-p encrypted-password
passes pre-ecnrypted password for the user to the system

default shell
-s shell
sets the name for the users default login shell

UID
-u UID
create an account with the specified user ID value
+ int > 500

Front 11

useradd parameter
system account creation
no user group

Back 11

system account creation
-r specifies the creation of a system account - an account with a value less than UID_MIN as def in /etc/login.defs

no user group
-n in some distos (Red Hat) the system creates a group with the same name as the specified username

Front 12

Suppose you’ve added a hard disk and mounted it as /home2. You want to create an account for a user named Sally in this directory and place her home directory on the new disk. You want to make the new user a member of the project1 and project4 groups, with default membership in project4. The user has also requested tcsh as her default shell. The following commands accomplish this goal:

Back 12

# useradd -d /home2/sally -g project4 -G project1,project4 -s /bin/tcsh sally
# passwd sally

Front 13

setting a password cmd

Back 13

passwd [-k] [-l] [-u [-f]] [-d] [-S] [username]

Front 14

passwd parameter
Update expired account
Lock account

Back 14

Update expired account
-k parameter indicates that the system should update an expired account

Lock account
-l parameter locks an account by prefixing the encrypted password with an exclamation mark (!)

Front 15

passwd parameter
Unlock accounts
Remove an account’s password
Display account information

Back 15

Unlock accounts
-u parameter unlock an account by removing a leading exclamation mark

Remove an account’s password
-d parameter removes the password from an account, rendering it a password-less

Display account information
-S option displays info about the password for the account

Front 16

This utility changes an existing account instead of creating a new one

Back 16

usermod program

differences between useradd and usermod are

usermod allows the addition of a -m parameter when used with -d. The -d parameter alone changes the user’s home directory, but it doesn’t move any files. Adding -m causes usermod to move the user’s files to the new location.

usermod supports a -l which changes the user’s login name to the specified value

You may lock and unlock a user’s password with the -L and -U options, respectively.

Front 17

Does changing the UID of an user account changes the UID stored with a user's file

Back 17

not

You can manually update the UIDs on all files by using the chown

# chown -R sally /home/sally

Front 18

command allows you to modify account settings relating to account expiration

Back 18

chage

It’s possible to configure Linux accounts so that they automatically expire if either of two conditions is true:
The password hasn’t been changed in a specified period of time.
The system date is past a predetermined time.

chage [-l] [-m mindays] [-M maxdays] [-d lastday] [-I inactivedays] [-E expiredate] [-W warndays] username

Front 19

chage parameters
display info
set the min time between pass changes
set the max time between pass changes

Back 19

display info
-l option
causes change to display account expiration and password agign info for a particular user

set the min time between pass changes
-m mindays
0 indicates multiple changes per day
1 once per day
2 and up twice and up

set the max time between pass changes
-M maxdays

Front 20

chage parameters
Set the last password change date
Set the maximum inactive days
Set the expiration date
Set the number of warning days

Back 20

Set the last password change date
-d lastday
last day a password was changed. This value is normally maintained automatically by Linux

Set the maximum inactive days
-I inactivedays
ets the number of days
between password expiration and account disablement

Set the expiration date
-E expiredate

Set the number of warning days
-W warndays
sets the number of days before account expiration that the system will warn the user of the impending expiration

Front 21

A typical /etc/passwd entry resembles the following

Back 21

sally:x:529:100:Sally Jones:/home/sally:/bin/bash

Username - Password - account user ID - default login group ID - comment - home dir - default shell

the x for password indicates that shadow passwords are in use

Front 22

An /etc/shadow line resembles the following:

Back 22

sally:E/moFkeT5UnTQ:14069:0:-1:7:-1:-1:

user name - password (stored on encrypted form) - last password change - day until change is allowed - day before the change is required - warning before expiration - day between activation/deactivation - expiration date - spacial flag

Front 23

cmd to delete an user account

remove user files option
force deletion option
get help

Back 23

userdel

remove user files option
-r/--remove
removes files from the mail spool and home dir

force deletion option
-f/--force
force deletion while user is still logger

get help
-h/--help

Front 24

if sally was UID 529, you can use the following command to locate all her files usefull when looking for all user files outside of home dir :

Back 24

# find / -uid 529

Front 25

removing users from Samba

Back 25

Samba keeps its own list of users

manually edit smbpasswd file usually in
/etc, /etc/sambe or /etc/samba.d

or

smbpasswd -x sally

Front 26

Linux provides the _____ command to add a new group

Back 26

groupadd [-g GID [-o]] [-r] [-f] groupname

Front 27

groupadd options

Specify GID
Create a sub-500 GID
Force creation

Back 27

Specify GID
-g GID parameter
when omited uses the next available GID

Create a sub-500 GID
-r parameter instructs groupadd to create a group with a GID of less than 500.

Force creation
-f parameter
if you try to create a group that already exists, groupadd returns an error message

Front 28

Group information, like user account information, may be modified either using

Back 28

utility programs
directly editing the /etc/group

Front 29

command modifies an existing group’s setting

Back 29

groupmod [-g GID [-o]] [-n newgroupname] oldgroupname

Front 30

cmd to add a user to a group

Back 30

usermod with -G

# usermod -G users,project1,project4 sally

ommiting any of the current user's group will remove the user from those groups

Front 31

discover the groups to which a user currently belongs with the _________ cmd

Back 31

groups cmd

groups sally

Front 32

cmd that allows you to modify group features and assign group admin

Back 32

gpasswd [-a user] [-d user] [-R] [-r] [-A user[,...]] [-M user[,...]] group

Front 33

gpasswd option
add a user
delete a user
disallow newgrp additions

Back 33

add a user
-a user

delete a user
-d user

disallow newgrp additions
-R option configures the group to not allow anybody to
become a member through newgrp

Front 34

gpasswd options
remove passowrd
add group admin
add users

Back 34

remove passowrd
-r option removes the password from a group.

add group admin
-A user[,...] parameter to specify group administrators

add users
-M user[,...]

Front 35

If entered without any parameters except a group name, gpasswd changes

Back 35

the password for the group. Group passwords enable you to control temporary membership in a group

Front 36

Group information is stored primarily in what file

Back 36

/etc/group

A typical line in this file resembles the following:
project1:x:501:sally,sam,ellen,george

group name - password - guid - user list

Front 37

Systems with shadow passwords also use another file, _________ to store shadow password information about groups.

Back 37

/etc/gshadow

Front 38

Deleting groups is done via

Back 38

groupdel command

groupdel project3

You can also delete a group by editing the /etc/group file (and /etc/gshadow, if present) and removing the relevant line for the group.
This is not recomended

Front 39

files in /etc are

Back 39

global configuration files, which affect all
users

Front 40

You can view all your current environment variables by typing

Back 40

env cmd

Front 41

location of skeleton dir

Back 41

/etc/skel

useradd copies files from the skeleton directory (/etc/skel by default) into a newly created home directory

Front 42

daemon def

Back 42

daemon is a program that runs continuously in the background waiting for an event to trigger it to perform some action

Front 43

main log deamon

Back 43

syslogd

often installed from a package called sysklogd

Front 44

syslogd daemon expl

Back 44

syslogd daemon handles messages from servers and other user-mode programs. It’s usually paired with a daemon called klogd, which is generally installed from the same sysklogd package as syslogd.

Front 45

klogd daemon

Back 45

manages logging of kernel messages

Front 46

syslog-ng

Back 46

daemon for logging that support advanced filtering options

Front 47

config for syslogd

config for rsyslog

Back 47

done through the /etc/syslog.conf file

rsyslogd configuration file is /etc/rsyslog.conf

Front 48

/etc/syslog.conf structure

Back 48

# comment line

facility.priority action

facility - code word for the type of program that generated the message

priority - code word for the importance of this message

action - file or remote pc that accepts the message

facility and priority are referred as selector

Front 49

Valid codes for the priority in /etc/syslog.conf

Back 49

debug, info, notice, warning, warn, error, err, crit, alert, emerg, panic.

warning = warn
error = err
emerg = panic

error, warn, panic are
deprecated

Front 50

Valid codes for the facility in /etc/syslog.conf

Back 50

auth, authpriv, cron, daemon, kern, lpr, mail, mark, news, security, syslog, user, uucp, local0 through local7.

An asterisk (*) refers to all facilities
multiple facilities in one selector by separating the facilities with commas (,).

Front 51

priority in /etc/syslog.conf special cahracters

Back 51

=crit
describes what to do with messages of cript priority only

*
all priorities

!crit

causes messages below crit priority to be logged

Front 52

priority in /etc/syslog.conf action

Back 52

facility.priority action

most times action point to a file

Front 53

typical directory tree for logs

Back 53

/var/log

messages, logs, secure are 3 common and importnat log files

Front 54

to display log messages on the screen what action target needs to be specified in /etc/syslog.conf

Back 54

/dev/console

Front 55

to display on remote machine what action target needs to be specified in /etc/syslog.conf

Back 55

a remote machine name preceded by an at sign (@) to log data to the specified system, and a list of usernames of individuals who should see the message if they’re logged in.

Front 56

line sends all log entries identified by the originating program as related to mail to the /var/log/mail file

Back 56

mail.* /var/log/mail

Front 57

line sends all emerg-level messages to the consoles of all users who are logged into the
computer using text-mode tools.

Back 57

*.emerg *

Front 58

logs all kernel messages to /var/log/kernel

sends critical messages to logger.pangaea.edu.

Back 58

kern.* /var/log/kernel

kern.crit @logger.pangaea.edu

Front 59

sends messages that are between info and err in priority to /var/log/kernel-info.

Back 59

kern.info;kern.!err /var/log/kernel-info

Front 60

to manually create a log entry or have a script do so use

Back 60

logger [-isd] [-f file] [-p pri] [-t tag] [-u socket] [message ...]

Front 61

logger options

Record logger PID
Output to standard error
Log using datagrams

Back 61

Record logger PID
-i
records ID of the logger process along with other data

Output to standard error
-s
echo data to standard error, as well as to the log file

Log using datagrams
-d
causes logger to use datagrams rather that a stream connection

Front 62

logger options

log a file
identify priority
log tags

Back 62

log a file
-f file

identify priority
-p pri
specifies priority

log tags
-t tag
by default logger includes its name in the log file as tag can be changed with this option

Front 63

logger options

specify socket
specify a message

Back 63

specify socket
-u socket
can log directly to a socket

specify a message
if you dont specify a file using -f file, logger will log whatever you type after other options as the message to be logged to terminate the input press Ctrl + D

Front 64

you want to log the message “shutting down for system maintenance” to the system log. You can do so by typing the following command:

Back 64

$ logger shutting down for system maintenance

The result will be an entry like the following, probably in /var/log/messages:
Jul 29 14:09:50 nessus logger: shutting down for system maintenance

Front 65

The most common log rotation tool is a package called

Back 65

logrotate

typically called on a regular basis via a cron job

Front 66

logrotate program consults a configuration file called

Back 66

/etc/logrotate.conf

includes several default settings and typically refers to files in /etc/logrotate.d to handle specific log files

Front 67

Manually Setting the Time main tool to set the software clock is

Back 67

date [-u|--utc|--universal] [MMDDhhmm[[CC]YY][.ss]]

without parameters displays current date

Front 68

utility enables you to set the hardware clock from the software clock or vice versa

show hardware clock option
set hardware clock manually

Back 68

hwclock [options]

show hardware clock option
-r --show

set hardware clock manually
--set --deat=newdate

Front 69

hwclock [options]

Set the hardware clock based on the software clock
Set the software clock based on the hardware clock
Specify UTC or local time

Back 69

Set the hardware clock based on the software clock
--systohc
if soft clock is set with --systohc you can set the hardware clock

Set the software clock based on the hardware clock
--hctosys
to set the software clock to the
hardware clock’s value

Specify UTC or local time
tell Linux to treat the hardware clock as storing UTC by using the --utc option or to treat it as holding local time by using the --localtime option

Front 70

SMB/CIFS

Back 70

Server Message Block/Common Internet File System

Front 71

ntp.drift

Back 71

usually in /var/lib/ntp but is sometimes stored in /etc.

Front 72

list NTP servers in linux

NTP config file

Back 72

ntp
xntp
ntpd
xntpd

/etc/ntp.conf. This file contains various NTP options, but the most important are the server lines

Front 73

Once you’ve made your changes, start or restart your NTP daemon. Typically, this is done via a SysV startup script:

Back 73

# /etc/init.d/ntpd restart

Front 74

differences between useradd and usermod

Back 74

- usermod allow -m when using -d
-d changes the sue's home dir, but doenst move any files
-m causes usermod to move the user's file to the new location

-usermod support -l
changes login name to specified value

Front 75

cmd that allow modification of account settings related to account expiration

Back 75

chage [-l] [-m mindays] [-M maxdays] [-d lastday] [-I inactivedays].
[-E expiredate] [-W warndays] username

Front 76

change -l ?

change -m ?

change -M ?

Back 76

change -l
displays account expiration and password aging info for an user

change -m minday
parameter sets the min number of days between password change; 1 once a day; 2 every two days

change -M maxday

Front 77

change -d

change -I

change -E

change -W

Back 77

change -d lastday
sets the last day pass was changed

change -I inactivedays
sets the number of days between pass expiration and account disablement

change -E expirdate
set an absolute expiration date

change -W warndays
sets the number of days before account expiration that the system will warn the user of the impeding expiration

Front 78

shutdown account def

Back 78

many systems include a shutdown account with /bin/shutdown as the shell
if you log in in this account it immediately shutsdown the system

Front 79

Account with shell of /bin/false (def)

Back 79

Account with shell of /bin/false prevents users from logging in as ordinary users but leave other utilities intact.
Users can still receive mail and retrieve it

Front 80

* or ! in /etc/shadow file

Back 80

the password is stored in encrypted format in /etc/shadow
! or * denotes and account with no password aka locked account that doesn't accepts login usually used by the system itself

Front 81

permission for ownership by root

Back 81

permission for ownership by root
rw - - - - - - -(600)
/etc/shadow is with this permission

rw-r--r-- (644) indicates that a file is readable by ordinary users

Front 82

omiting -r in # userdel -r sally

Back 82

You may omit the -r parameter if you want to preserve the user’s files

Front 83

most common way of creating groups

Back 83

without specifying any parameters but name

#groupadd projects3

Front 84

what useradd does with dir _________ when creating new users

Back 84

useradd copies files from the skeleton directory /etc/skel into a newly created home dir

Front 85

rsyslog (expl)

Back 85

recent version of Fedora use this rsyslogd demon

Front 86

using tail to monitor file on an ongoing basis (cmd)

Back 86

tail -f /var/log/meesages

Front 87

UTC
GMT (abbr)

Back 87

UTC - Coordinated Universal Time
GMT - Greenwhich Mean Time

Front 88

Example set the time to 3:02 pm on October 27,2009 by using the following cmd

Back 88

date 102715022009

Front 89

Options and cmd to use to set clock in UTC

Back 89

date cmd with -u, --utc or --universal

Front 90

ntp.drift file

Back 90

NTP doesn’t just reset the system clock periodically;
the server improves the accuracy of the system clock. In part, this is done through the ntp.drift file, which is usually buried in /var/lib/ntp but is sometimes stored in /etc. This file holds information about the software clock’s inaccuracies and so can be used to
correct for them.

Front 91

to verify that NTP is working use _________ cmd

Obtain NTP server list cmd

Back 91

ntpq

ntpq -q

Front 92

You may want to ensure that your NTP clients can’t be accessed as servers. This is a security measure. You can do this with an ______________ firewall rule or by using the _____________ line in ntp.conf

Back 92

iptables firewall rule

restrict default ignore line in ntp.conf. This line tells the server to ignore all incoming NTP requests.

Front 93

ntpdate cmd

Back 93

a simpler way to set the time on a client
part of the NTP suite
performs a one-time clock setting

#ntpdate clock.example.com

Front 94

ntpd switch equivalte to ntpdate

Back 94

-q

ntpd -q
enables it to perform a one-time clock setting to a values that's wildly divergent from the current time

Front 95

folder containing temp files created by users

Back 95

/tmp

Front 96

cron def

Back 96

a program daemon, running continuously, responding to temporal events.
Wakes up once a minute and examines config files in /var/spool/cron and /etc/cron.d directories and the /etc/crontab file, and executes commands
specified by these configuration files if the time matches the time listed in the files

Front 97

conf file used by cron (list ?)

Back 97

/var/spool/cron
/etc/cron.d
/etc/crontab

Front 98

two types of cron jobs (list ?)

Back 98

system cron jobs - run as root and perform system-wide maintenance tasks
user cron jobs - ordinary users can create user cron jobs which can run some user program on a regular basis

Front 99

what file controls system cron jobs

Back 99

/etc/crontab

usually begins with several lines that set environmental var such as $PATH and $MAILTO

Front 100

/etc/crontab sample line

Back 100

02 4 * * * root run-parts /etc/cron.daily

first 5 fields spec. time
min-hour-dayofmont-month-dayofweek
* - matches all possible values
- "dash" indicates range of values
/ "slash" in conjuction with other multi-value options, specifies stepped values - */10 means every 10 min
6th field is account name to be used when exec the prog
7th cmd to be run "run-parts /etc/cron.daily"

Front 101

most distributions include monthly, daily, weekly and hourly system cron jobs each corresponding to scripts in a directory called ________ + alternative for other distros _______

Back 101

/etc/cron.interval

where interval is a word associated with the run frequency

other distro palce the, in /etc/cron.d/interval

Front 102

to create a user cron job use _____ utility

Back 102

crontab
(not to be confused with the /etc/crontab config file)

crontab [-u user] [-l | -e | -r] [files]

Front 103

crontab modifiers
-u
-l
-e
-r
[files]

Back 103

crontab modifiers
-u user
modifies the cron job associated with the current user

-l
causes crontab to display the current cron job

-r
removes the current cron job

-e
opens and editor to edit the current crom job

[files] you can create a cron job config file and pass the file name to crontab
crontab -u tbaker my-cron
crontab will use my-cron as settings fro tbaker job

Front 104

Sample cron job

Back 104

SHELL=/bin/bash
MAILTO=tbaker
HOME=/home/tbaker
0,30 * * * * /usr/bin/fetchmail -s
0 2 * * mon /usr/local/bin/clean-adouble $HOME

Front 105

location for user cron job

Back 105

/var/spool/cron
/var/spool/cron/tabs
/var/spool/cron/crontabs

Front 106

Users who should be able to schedule jobs using cron should be added to what group

Back 106

cron
but check owner and permission on the
/user/sbin/cron
/usr/sbin/crontab

Front 107

cron allowed users are listed in what file
cron disallowed users are listed in what file

Back 107

/etc/cron.allow
/etc/cron.deny

Front 108

anacron def

Back 108

cron is great for systems that don't get turned off
acron keeps a record of programs it should execute and how frequently it should (in days)
when acron is ran it check to see if programs execution interval has passed
usually started with startup script

Front 109

anacron config file

Back 109

/etc/anacrontab

this file consist of comments, environmental variable set lines and job definition lines

job def. line: period delay identifier command
delay between anacron start and when job is executed

Front 110

sample anacron file /etc/anacrontab

Back 110

SHELL=/bin/bash
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
# format: period delay job-identifier command
1 5 cron.daily run-parts /etc/cron.daily
7 10 cron.weekly run-parts /etc/cron.weekly
30 15 cron.monthly run-parts /etc/cron.monthly

Front 111

start up script to run cron

Back 111

SysV startup scirpt with no options that runs anacron should be config to run from your regular runlevel
OR
palce a call to anacron to local startup script like
/etc/rc.d/rc.local - Feodra/RedHat
/etc/boot.d/boot.local - Suse

Front 112

at cmd expl

Back 112

when you want to run a single cmd at a specific point in the future on a one-time bases user at cmd

Front 113

at HH:MM

Back 113

at takes a single option time

at HH:MM
at MMDDYY, MM.DD.YY or MM/DD/YY

Front 114

at cmd daemon is

Back 114

atd
at relies on it to be running
if your system doesn't start atd automatically, you may need to configure a SysV startup

Front 115

What
at -f commands.sh noon
does?

Back 115

use the contents of commands.sh as the commands you want to run at noon

Front 116

Quit at cmd promt with what short cut

Back 116

Ctrl + D

Front 117

atq cmd
atrm cmd

Back 117

atq - list pending at jobs
atrm - removes an at job from the queue

Front 118

at cmd access restriction

Back 118

/etc/at.allow
/etc/at.deny

if neither exist only root can use at cmd