chmod
to change access mode of a file (file permissions)
u = the user who owns the file
g = the group the file belongs to
o = others
a = all of the above (ab abbreviation for ugo)
example: to prevent outsiders from executing archive.sh before : -rwxr-xr-x archive.sh
command: chmod o=r archive.sh
after : -rwxr-xr-- archive.sh
example : to take away all permissions for the group for topsecret.inf, leave the permissions part of the command empty.
Before : -rw-r----- topsecret.inf
command : chmod g= topsecret.inf
after : -rw------- topsecret.inf
example:
chmod go=rx wordmatic.txt
chmod go-w wordmatic.txt
chmod a+wx calcmatic.bak
To kill non responding application:
ctrl-alt-Esc
move or rename files:
mv
whatis
information on a topic
makewhatis
creates an updated whatis database
umask
the default permission given to new files created
suid and sgid
special permissions given to program so when it runs by a user, it inherits the rights of the owner of the pprogram, not the user running it.
eg. /etc/passwd
setting & removing suid & sgid
for eg.:
# chmod u+s /usr/bin/myapp
# chmod g-s /home/drobbins
Directory permissions:
Directory permissions are a bit different that file permissions.
For a directory, if the “read” (r)flag is set, you may list the contents of the directory.
“write” (w) means you may create files in the directory; and “execute” (x) means you may enter the directory and access any sub-directory inside.
Without the “execute” (x) flag, the filesystem objects inside the directory aren't accessible.
Without the “read” ( r ) flag, the filesystem objects inside the directory aren't viewable but can still be accessible as long as someone knows the full path to the object.
If a directory has the “sgid” flan enabled, any filesystem objects created inside it will inherit the group of the directory. This particular feature come in handy when you need to create a directory tree to be used by a group of people that all belong to the same group.
simply do this:
# mkdir /home/groupspace
# chgrp mygroup /home/groupspace
#chmod g+s /home/groupspace
now any users in the group mygroup can creat files or directories inside /home/groupspace, and they will be automatically assigned a group ownership if mygroup as well. Depending on the users' umask settings, new filesystem objects may or may not be readable, writable, or executable by other members of th mygroup group.
after installing Windows server 2003 on an available partition, the previous grub was destroyed from from MBR by Windows.
solution:
restart from rescue cd
reinstall grub: /sbin/grub-install /dev/hda
symbolic link:
ln -s [target] [link_name]
rsync
eg.:
rsync -av –delete /home/user/ username@server:/backup/home/user
If a directory is being backed up, remember to use / at the end of the directory name.
rsync uses ssh
Users & Groups
newgrp
useradd
groupadd
usermod
userdel -r (-r to remove user home directory too)
groupdel
ACL
acl shou be in the /etc/fstab
# getfacl
# setfacl
VNC
start vnc server:
vncserver
change password:
vncpasswd
connect to server from client by specifying the ip address/hostname and desktop
eg.:
192.168.123.10:1
configuration file:
.vnc/xstartup
default window manager is TWM, you can change it
eg.:
startkde or startgnome
to kill vnc:
vncserver -kill :1
default vnc viewer port: 5901
Java based viewer: 5801
