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Command Reference - Linux
Ctrl+R - To search your bash history
Kill -9 processno - To force kill the process who own
/etc/init.d/postgres/apache/mysql -restart/-stop/-start - To restart the services. you should be logged in as root to do that
Environment Control
Command Description
cd d Change to directory d
mkdir d Create new directory d
rmdir d Remove directory d
mv f1 [f2...] d Move file f to directory d
mv d1 d2 Rename directory d1 as d2
passwd Change password
alias name1 name2 Create command alias (csh/tcsh)
alias name1="name2" Create command alias (ksh/bash)
unalias name1[na2...] Remove command alias na
ssh nd Login securely to remote node
exit End terminal session
setenv name v Set env var to value v (csh/tcsh)
export name="v" set environment variable to value v (ksh/bash)
Output, Communication, & Help
Command Description
lpr -P printer f
or
lp -d printer f Output file f to line printer
script [f] Save terminal session to f
exit Stop saving terminal session
mailx username Send mail to user
man name Unix manual entry for name
Process Control
Command Description
CTRL/c * Interrupt processes
CTRL/s * Stop screen scrolling
CTRL/q * Resume screen output
sleep n Sleep for n seconds
jobs Print list of jobs
kill % Kill job n
ps Print process status stats
kill -9 n Remove process n
CTRL/z * Suspend current process
stop %n Suspend background job n
cmmd& Run cmmd in background
bg [%n] Resume background job n
fg [%n] Resume foreground job n
exit Exit from shell
Environment Status
Command Description
ls [d] [f...] List files in directory
ls -1 [f...] List files in detail
alias [name] Display command aliases
printenv [name] Print environment values
quota Display disk quota
date Print date & time
who List logged in users
whoami Display current user
finger [username] Output user information
chfn Change finger information
pwd Print working directory
history Display recent commands
! n Submit recent command n
File Manipulation
Command Description
vi [f] Vi fullscreen editor
emacs [f] Emacs fullscreen editor
ed [f] Text editor
wc f Line, word, & char count
cat f List contents of file
more f List file contents by screen
cat f1 f2 >f3 Concatenates f1 & f2 into f3
chmod mode f Change protection mode of f
cmp f1 f2 Compare two files
cp f1 f2 Copy file f1 into f2
sort f Alphabetically sort f
split [-n] f Split f into n-line pieces
mv f1 f2 Rename file f1 as f2
rm f Delete (remove) file f
grep 'ptn' f Outputs lines that match ptn
diff f1 f2 Lists file differences
head f Output beginning of f
tail f Output end of f
Compiler
Command Description
cc [-o f1] f2 C compiler
lint f Check C code for errors
f77 [-o f1] f2 Fortran77 compiler
pc [-o f1] f2 Pascal compiler
Comparing files and email output
sdiff/diff file1 file2 | mail emailaddress@mail.com -c ccemailaddress -s \"subject details\"";
How to log in as apache if you can't
If when you do:
su apache
you get "This account is currently not available." then it's probably because that account doesn't have a shell.
You can get around this with:
su -s /bin/bash apache
(or use the shell of your choice)
Running MS-DOS commands without displaying a window (vbscript)
This actually does work as a way of running a command (for example, as a Scheduled Task), without displaying that annoying MS-DOS command window at all (not even for a second).
Create this very short vbscript and name it something like "my_script.vbs". You can then double-click that script to run it without displaying an output window or you can add that script directly to Task Scheduler.
The script should look like this:
--- start of script ---
' Command to run:
cmd = "c:mycommand.exe arg1 arg2"
' Run the command. The "0" makes the command run in a hidden window.
Set WshShell = WScript.CreateObject("WScript.Shell")
WshShell.Run cmd, 0
--- end of script ---
Setting up per-user access on vsftpd
You need to use the user_config_dir config option in your vsftpd.conf file (which is probably in /etc/vsftpd).
1. Create a dir where you can put user config files (for example /etc/vsftpd/user_configs/).
2. Add the line "user_config_dir=/etc/vsftpd/user_conf/" somewhere in your vsftpd.conf file (I added it at the end but probably it would work anywhere).
3. For EVERY user that needs to use the ftp server, there now needs to be a file matching their username in the user config dir. So if "john" used to log in via ftp, now you need to set up the file "/etc/vsftpd/user_configs/john". It can contain one or more of the config options from your main vsftpd.conf (although not all options are supported on a per-user level - see man pages).
4. If you want users to have the "default" ftp options, make their config file a symbolic li
nk to the main vsftpd.conf. For example, if we want the user "john" to have the default actions, make a symbolic link to /etc/vsftpd/vsftpd.conf called /etc/vsftpd/user_configs/john. If there's no config file or symbolic link called "john" in the user config dir then then john will get an error when he tries to connect.
5. Restart vsftpd for the settings to take effect:
/etc/init.d/vsftpd reload
Running MS-DOS commands in the background
You can use the "start" command like this:
start /B my_command
Putty problem - Unable to use key file (SSH1 private key)
If you get this message and you have already set up the SSH keys correctly, make sure that Putty is set to use the correct SSH version (1 or 2). If it's using SSH 2 and the the keys you have set up are for SSH 1 then the automatic authentication wont work and you will get the message Unable to use key file. You can change the type of SSH Putty uses in the program options for each saved session.
starting proftp
/usr/local/sbin/proftpd start
cron field order
minute, hour, day-of-month, month, day-of-week, command
Note that day-of-week is 0 = Sunday
Getting putty working using SSH keys
1. Setting up OpenSSH:
The server needs to be set up to accept ssh keys access. In the OpenSSH config file (/etc/ssh/sshd_config) I used the following options (note that some of these options may be the default, therefore they would not need to be explicitly specified... but these are the lines I changed):
StrictModes no
RSAAuthentication yes
PubkeyAuthentication yes
AuthorizedKeysFile .ssh/authorized_keys
After updating the config file, restart the service:
service sshd stop
service sshd start
2. Setting up putty:
2.1. Getting the public and private keys:
Using puttygen.exe:
- Select SSH1 (RSA) as the type of key.
- Use 1024 as the number of bits generated.
- Click 'generate' and move the mouse about to generate the key.
- Enter a key comment, such as "rangi
.robinson_desktop" (whatever you want).
- Enter and confirm a key phrase (should be hard to guess).
- Save the private key as a file on your machine.
Using pageant.exe:
- Select 'Add key'.
- Open the private key file you saved on your machine.
- Enter your key phrase (you have to do this whenever pageant.exe is started).
The program pageant.exe keeps your private key in memory until it's closed, so whenever putty tries to connect to the server, it attempts to use the private key signature for authorisation.
3. Putting your private key on the server:
- Log into your account via putty (using a password).
- In your home directory:
mkdir .ssh
chmod 700 .ssh
cd .ssh
touch authorized_keys
vi authorized_keys
- Copy and paste your entire public key from puttygen.exe to the authorized_keys file.
- Save and close the authorized_keys file.
You should now be
able to log into the server with putty using just the ssh key, no username and password required. If it's not working, try restarting sshd, as above.
Useful links:
http://www.openssh.com/ OpenSSH website/docs
http://www.chiark.greenend.org.uk/~sgtatham/putty/ Putty website/docs
http://cvs.datafox-engineering.com/#top Tutorial on this subject
Unix user/file admin:
chown - change the owner of a file/dir
chown rangi myfile
chgrp - change the group of a file/dir
chgrp
useradd - add a user to the system
useradd -d /home/johnny johnny
After adding a user, you must add a password to thier account before they can use it.
passwd - change/set password
passwd johnny - change johnny's password
passwd - change your own password
userdel - delete a user
userdel johnny - delete the 'johnny' user
userdel -r johnny - delete the 'johnny' user and his home dir
Get a list of users on the system:
more etc/passwd
inodes
inodes are data structures that contain information about files in Unix file systems. Each file has an inode and is identified by an inode number (i-number) in the file system where it resides. inodes provide important information on files such as user and group ownership, access mode (read, write, execute permissions) and type.
inodes are created when a file system is created. There are a set number of inodes, which indicates the maximum number of files the system can hold.
A file's inode number can be found using the ls -i command, while the ls -l command will retrieve inode information.
Get disk usage numbers:
df -h
or if that doesn't work:
df -bk
Enable directory browsing in Apache:
Add this directive to httpd.conf
Options Indexes
Note that the path is the full file system path, not the path relative to
the web root dir.
Then restart Apache:
/etc/rc.d/init.d/httpd restart
This all works fine on the HC remote server.
Linux set path (append path to existing path)
PATH=$PATH:/new/path
Restart Apache (2 methods)
/etc/rc.d/init.d/httpd restart
Or
/usr/local/apache/bin/apachectl restart
Find out what symbolic links are pointing to:
ls -l
Add a watermark to image with ImageMagick
composite -compose bumpmap -gravity southeast watermark.png input.jpg output.jpg
Also, take a look at the -watermark option (this may well do this better).
Linux user admin
Create user rangi and specify home directory:
useradd rangi -d /usr/local/rangi
Set password for rangi
passwd rangi
Create group called chacha
groupadd chacha
Add users to a group
usermod -G chacha rangi
Background commands
If you wish to run a command in the background, follow it with an ampersand, so kedit & will launch the kedit application and return you to the command prompt without waiting for the application to finish.
Create an empty test file on Linux
This creates a 3gig file called myfile.
dd if=/dev/zero of=myfile bs=1M count=3072
Using Linux TSQL (from FreeTDS) to query MS SQL Se
Using Linux TSQL (from FreeTDS) to query MS SQL Server database on Windows.
Conf file being used with this installation is /usr/local/etc/freetds.conf. The
file contains the following server entry:
[HCSERVER]
host = 192.168.157.1 (IP of Windows machine)
port = 1433 (The normal port for MS SQL Server)
This allows us to connect from the command line using:
tsql -S HCSERVER -U rangi
Where rangi is a user and login in SQL Server.
NOTES
If getting an error message like "server does not exist or is not available" when
trying to connect then do the following.
Go into SQL Server Enterprise Manager.
Right-click the server that we are trying to connect to, select properties.
In the Security tab, make sure the authenticaion type is
"SQL Server and Windows" (not "Windows only")
Click OK to exit the dialog box.
In the tree navigator below the server, choose security->logins.
Make sure the user name we are connecting with is present, and they are using 'SQL Server' Authentication.
If not create it (the user must be based on a Windows user - so you might have to create one (control panel -> users))
If yes, re-enter the password.
Restart SQL Server.
You should now be able to connect.
No FTP/HTTP between Windows and Linux (ping workin
CAUSES
Hardware - if ping is working this is not the problem
Subnet - check that computers are on same subnet
Firewall - check that not enabled - config and startup files, see below.
Services running - Check running, check ports, check run levels
SOLUTIONS
Red hat (or other dist) manual
Search error messages online
Compare config with working machine
Reinstall with no firewall and gnome installed (so can use gnome-lokkit)
NOTES
I have had a case where all of these have been checked and nothing works. Then I come back the next day and it works... why I don't know.
Check subnet with ipconfig (win) and ifconfig(lin).
Red hat online manual networking section is useful for looking up programs
to specify which services are running, starting them stopping them and
choosing if they are
started/stopped at different run levels. On a
graphical desktop, "serviceconf" in a console is good. The console
alternative is "netsysv", although with that one you can only edit one
run level. "chkconfig" can be used to start/stop individual services and
choose what run levels they run at. The Red hat online manual has a good
explanation of these.
Wu-fptd runs as an xinetd service. The line "disable no"
should be in /etc/xinetd.d/wu-ftpd (not "disable yes").
xinetd is restarted with "service xinetd restart".
ipchains and iptables can be disabled (I think) with:
chkconfig --level 0123456 ipchains off
chkconfig --level 0123456 iptables off
The --level is used to specify the run levels.
When it _does_ work, if the FTP connection is slow to start, try turning
off 'passive mode' in the FTP client.
xinetd
Restart xinetd with:
service xinetd restart
Setting and reading bash env vars
export myvar=myvalue (sets env var)
echo $myvar (echos env var)
inet/xinet services
Getting access to inet/xinet services from hosts other than localhost:
1. Ensure there is nothing in hosts.allow/deny that would deny the user
2. Check firewall. This can be disabled for testing by typing
lokkit
and choosing 'none'.
Also, see the problem below "No FTP/HTTP between Windows and Linux".
wu-ftp
Getting wu-ftp to work:
Make sure that etc/xinetd.d/wu-ftpd doesn't have the line
disable = yes
set. It must read:
disable = no
After making any changes to the config files you should restart xinetd:
/etc/init.d/xinetd restart
Try
ftp localhost
to test.
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