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useradd
user_name
passwd user_name
(as root) Create a new account (you must be root). E.g., useradd
barbara Don't forget to set up the password for the new user
in the next step. The user home directory (which is created) is /home/user_name.
You may also use an equivalent command adduser user_name
ls -l
/home/peter
useradd peter -u 503 -g 503
(as root). Create an account to match an existing directory (perhaps
from previous installation). If the user ID and the group ID (shown
for each file) were both 503, I create an account with a matching user
name, the user ID (UID) and the group ID (GID). This avoids the
mess with changing the ownership of user files after a system upgrade.
userdel
user_name
Remove an account (you must be a root). The user's home directory and
the undelivered mail must be dealt with separately (manually because you
have to decide what to do with the files). There is also groupdel
to delete groups.
groupadd
group_name
(as root) Create a new group on your system. Non-essential on a home machine,
but can be very handy even on a home machine with a small number of users.
For
example, I could create a group "friends", using
groupadd friends
then edit the file /etc/group, and add my login name and the
names of my friends to the line that lists the group, so that the final
line might look like this:
friends:x:502:stan,pete,marie
Then, I can change the permissions on a selected file so that the file
belongs to me AND the group "friends".
chgrp friends my_file
Thus, the listed members of this group have special access to these files
that the rest of the world might not have, for example read and write
permission:
chmod g=rw,o= my_file
The alternative would be go give write permission to everybody, which
is definitely unsafe even on a home computer.
groups
List the groups to which the current user belongs. Or I could use groups
john to find to which groups the user john belongs.
usermod
groupmod
(as root) Two command-line utilities to modify user accounts and groups
without manual editing of the files /etc/passwd /etc/shadow /etc/group
and /etc/gshadow. Normally non-essential.
userconf
(as root) Menu-driven user configuration tools (password policy, group
modification, adding users, etc). Part of linuxconf package, but can be
run separately.
passwd
Change the password on your current account. If you are root, you can
change the password for any user using: passwd user_name
chfn
(="change full name"). Change the information about you (full name, office
number, phone number, etc). This information is displayed when the finger
command is run on your login_name.
chage
-M 100 login_name
(= "change age"). Set the password expiry to 100 days for the user named
login_name .
quota
username
setquota username
quotaon /dev/hda
quotaoff /dev/hda
A set of commands to manage user disk quotas. Normally not used on a home
computer. "Disk quota" means per-user limits on the usage of disk
space. The commands (respectively) display the user quota, set the user
quota, turn the quota system on the for a given filesystem (/dev/hda in
the above example), turn the quota system off. "Typical" Linux distros
I have seen set on default: no limits for all users, and the quota system
is off on all filesystems.
kuser
(as root, in X terminal) Manage users and groups using a GUI. Nice
and probably covering most of what you may normally need to manage user
accounts.
chmod
perm filename
(=change mode) Change the file access permission for the files you own
(unless you are root in which case you can change any file). You can make
a file accessible in three modes: read (r), write (w), execute (x) to
three classes of users: owner (u), members of the group which owns the
file (g), others on the system (o). Check the current access permissions
using:
ls -l filename
If the file is accessible to all users in all modes it will show:
rwxrwxrwx
The first triplet shows the file permission for the owner of the file,
the second for the group that owns the file, and the third for others
("the rest of the world"). A "no" permission is shown as "-".
When setting permissions, these symbols are used: "u"(=user or owner of
the file), "g"(=group that owns the file), "o"(=others), "a" (=all, i.e.,
owner, group and others), "="(=set the permission to), "+"(=add the permission),
"-"(=take away the permission), "r"(=permission to read the file), "w"=(write
permission, meanning the permission to modify the file), "x"(=permission
to execute the file).
For
example, this command will add the permission to read the file
junk to all (=user+group+others):
chmod a+r junk
This command will remove the permission to execute the file junk
from others:
chmod o-x junk
Also try here
for more info.
You can set the default file permissions for the new files that you create
using the command umask (see man umask).
chown
new_ownername filename
chgrp new_groupname filename
Change the file owner and group. You should use these two commands after
you copy a file for use by somebody else. Only the owner of a file
can delete it.
lsattr
files
List attributes for the file(s). Not very often used because the most
interesting attributes are still not implemented. The attributes can be
changed using the chattr command. The attributes are: A (=don't
update atime when the file is modified), S (=synchronous updates),
a (=append only possible to this file), c (=file compressed on the kernel
level, not implemented yet), i (=immutable file), d (=no dump),
s (=secure deletion), and u (undeletable, not implemented yet). An interesting
usage may be to make a file undeletable even by root (until s/he clears
the attribute).
sudo
/sbin/shutdown -h now
(as a regular user, I will be prompted for my user password) Run the command
"shutdown" (or another command which you have been given permission to
run by your system administrator). With sudo, the administrator can give
selected users the rights to run selected commands, without handing out
the root password. The file /etc/sudoers must be configured
to contain something like:
my_login_name my_host_computer_name = /sbin/shutdown
pwck
grpck
(as root, two commands). Verify the integrity of the password and group
files.
pwconv
grpconv
(as root) Unlikely you need these commands. They convert old-style password
and group files to create the more-secure "shadow" files.
Next > 5.15 Program installation
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