UNIX trics

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Some useful tips and tricks for UNIX.

Command Reference[edit]

The UNIX Command Reference has nearly all the frequently used UNIX commands.

Profile[edit]

If you like a prompt like:
HarmFrielink@L3AFY65 ~
$
Place this PS1 into the  .bashrc  file (UNIX Escape Sequence) Together with the folowing options:

PS1="\[\e]0;\w\a\]\n\[\e[32m\]\u@\h \[\e[33m\]\w\[\e[0m\]\n\$ "

alias dir='ls --color=auto --format=vertical'         # DOS dir
alias ll='ls -l --group-directories-first --color'    # long list
alias la='ls -Al --group-directories-first --color'   # all but . and ..
alias l='ls -CF'                                      #

If running the bashrc is not possible because the error bash: /home/chris/.bashrc: Permission denied occurs perform the following statement:
 chmod 740 ./.bashrc  or better  chmod o+rwx ./.bashrc , see below for detailed info.

An alternative PS1 prompt:

 \w:\u\$

This will produce outcome like the current directory and username:

 /Projects/xx/yy:UserName$

See for more http://bash.cyberciti.biz/guide/Changing_bash_prompt.

ls & chmod[edit]

The meaning of the different colors in  ls --color  in combination with the  drwxrwxrwx  :

File Type Owner Access Group Access Other Access
-
d
regular file
directory
r
w
x
read
write
execute
r
w
x
read
write
execute
r
w
x
read
write
execute

The following example shows a directory for which the owner has read/write/execute access, the group has read/execute access, and all others have no access:

  drwxr-x---
File Access Descriptor
Entity Operator Access Rights
u
g
o
a
user(owner)
group
others
all of the above
+
-
=
grant
revoke
set
r
w
x
read
write
execute
chmod examples
Command Description
chmod u+rwx,g-rxw,o-rwx hosts Add all rights for owner and revoke all rights for group and others on the "hosts" file.
chmod g+r hosts Now add read access for the group.

Escape Sequence[edit]

More...

Errors[edit]

If you get the error The procedure entry point sigset could not be located in the dynamic link library cygwin1.dll install cygwin again.


SSH Keep Alive[edit]

When I close my MacBook with an active SSH session in Terminal and then wake it up, the prompt goes unresponsive. In about five minutes it says

Write failed: Broken pipe

and terminates.

For keeping the connection alive, you can check in /etc/ssh_config the line where it says ServerAliveInterval, that tells you how often (in seconds) your computer is gonna send a null packet to keep the connection alive. If you have a 0 in there that indicates that your computer is not trying to keep the connection alive (it is disabled), otherwise it tells you how often (in seconds) it is sending the aforementioned packet. Try putting 120 or 240, if it is still killing your connection, you can go lower, maybe to 5, if with that number it doesn't happen, maybe it is your router who is dumping the connection to free memory.

For killing it when it gets hang up, you can use the ssh escape character:

~.

That is, press the tilde and then the period, if it doesn't work, press Enter before you press that, that will kill the connection immediately.

UNIX Tutorials[edit]

See also[edit]

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