ssh $HOST lsTo run two commands on a remote server over SSH:
ssh $HOST 'ls; pwd'To run the third, fourth, fifth, etc. commands on a remote server over SSH keep appending commands with a semicolon inside the single quotes.
#!/bin/bash
ssh $HOST '
ls
pwd
if true; then
echo "This is true"
else
echo "This is false"
fi
echo "Hello world"
'
The above shell script works but begins to break if local variables are added.#!/bin/bash
HELLO="world"
ssh $HOST '
ls
pwd
if true; then
echo $HELLO
else
echo "This is false"
fi
echo "Hello world"
'
In order to parse the local variable #!/bin/bash
HELLO="world"
ssh $HOST bash -c "'
ls
pwd
if true; then
echo $HELLO
else
echo "This is false"
fi
echo "Hello world"
'"
Perhaps you want to use a remote sudo command within the shell script:#!/bin/bash
HELLO="world"
ssh $HOST bash -c "'
ls
pwd
if true; then
echo $HELLO
else
echo "This is false"
fi
echo "Hello world"
sudo ls /root
'"
When the above shell script is run, everything will work as intended until the remote sudo command which will throw the following error:sudo: sorry, you must have a tty to run sudoThis error is thrown because the remote sudo command is prompting for a password which needs an interactive tty/shell. To force a pseudo interactive tty/shell, add the
#!/bin/bash
HELLO="world"
ssh -t $HOST bash -c "'
ls
pwd
if true; then
echo $HELLO
else
echo "This is false"
fi
echo "Hello world"
sudo ls /root
'"
With a pseudo interactive tty/shell available, the remote sudo command’s password prompt will be displayed, the remote sudo password can then be entered, and the contents of the remote root’s home directory will be displayed.#!/bin/bash ssh $HOST bash -c "' cat << EOFTEST1 > /tmp/test1 line one line two line three line four EOFTEST1 cat << EOFTEST2 > /tmp/test2 line two EOFTEST2 sed -i -e '/line one/,+3 d' /tmp/test1 sed -i -e '/^line two$/i line one' /tmp/test2 '"Everytime I would run the above shell script, I would get the following error:
sed: -e expression #1, char 5: unterminated address regexHowever, the same commands work when run by themselves:
ssh $HOST "sed -i -e '/line one/,+3 d' /tmp/test1" ssh $HOST "sed -i -e '/^line two$/i line one' /tmp/test2"I thought the problem may be because of single quotes within single quotes. The
#!/bin/bash ssh $HOST bash -c "' echo "Hello" >> /tmp/test3 sed -i -e 's/Hello/World/g' /tmp/test3 '"I can only assume the problem with the specific remote sed commands is something with the syntax that I have not yet figured out.
ssh $HOST << EOF cat << EOFTEST1 > /tmp/test1 line one line two line three line four EOFTEST1 cat << EOFTEST2 > /tmp/test2 line two EOFTEST2 sed -i -e '/line one/,+3 d' /tmp/test1 sed -i -e '/^line two$/i line one' /tmp/test2 EOFDespite the remote sed commands working, the following warning message was thrown:
Pseudo-terminal will not be allocated because stdin is not a terminal.To stop this warning message from appearing, add the
ssh -T $HOST << EOF cat << EOFTEST1 > /tmp/test1 line one line two line three line four EOFTEST1 cat << EOFTEST2 > /tmp/test2 line two EOFTEST2 sed -i -e '/line one/,+3 d' /tmp/test1 sed -i -e '/^line two$/i line one' /tmp/test2 EOFWith this working, I later discovered remote sudo commands that require a password prompt will not work with HERE documents over SSH.
ssh $HOST << EOF sudo ls /root EOFThe above ssh command will throw the following error if the SSH user you are logging into requires a password when using the remote sudo command:
Pseudo-terminal will not be allocated because stdin is not a terminal. user@host's password: sudo: no tty present and no askpass program specifiedHowever, the remote sudo command will work if the SSH user’s sudo settings allow that user to use sudo without a password by setting
# lsitab init: init:2:initdefault:
/etc/rc.d /etc/rc.d/rc2.d /etc/rc.d/rc3.d /etc/rc.d/rc4.d /etc/rc.d/rc5.d /etc/rc.d/rc6.d /etc/rc.d/rc7.d /etc/rc.d/rc8.d /etc/rc.d/rc9.d
l2:2:wait:/etc/rc.d/rc 2 l3:3:wait:/etc/rc.d/rc 3 l4:4:wait:/etc/rc.d/rc 4 l5:5:wait:/etc/rc.d/rc 5 l6:6:wait:/etc/rc.d/rc 6 l7:7:wait:/etc/rc.d/rc 7 l8:8:wait:/etc/rc.d/rc 8 l9:9:wait:/etc/rc.d/rc 9
telinit
run level 2 Oct 4 14:23 2 0 S
Offering
|
Description
|
Capacity Upgrade on Demand
|
You can permanently activate inactive
processors and memory units with code without restart of server
|
Trial Capacity on Demand
|
You can evaluate the use of inactive processors, memory, or
both, at no charge using Trial CoD. After it is started, the trial period is
available for 30 power-on days.
|
On/Off Capacity on Demand
|
You can activate processors or memory units for a number of
days by using the HMC to activate resources on a temporary basis.
|
Utility Capacity on Demand
|
Utility CoD is used when you have
unpredictable, short workload spikes.
|
Capacity BackUp
|
You can use Capacity BackUp to provide an off-site, disaster
recovery server using On/Off CoD capabilities.
|
PowerVM™ Editions (PowerVM)
|
PowerVM Editions (PowerVM Editions) deliver advanced
virtualization functions
for AIX®, Linux® and IBM i™ clients.
PowerVM Editions (PowerVM Editions) include the following
offerings:
Ø Micro-Partitioning™
Ø Virtual I/O Server
Ø Integrated Virtualization Manager
Ø Live Partition Mobility
Ø The ability to run x86 Linux applications on Power Systems
PowerVM Editions (Express, Standard, and Enterprise) offer different capabilities.
|
Quotes
|
Name
|
Meaning
|
"
|
Double Quotes
|
"Double Quotes" - Anything enclose in double quotes removed meaning of that characters (except \ and $).
|
'
|
Single quotes
|
'Single quotes' - Enclosed in single quotes remains unchanged.
|
`
|
Back quote
| `Back quote` - To execute command |
#!/bin/sh
# show script
if [ -d $1 ]
then
ls $1
else
cat $1
fi
Here, we notice a number of points:
Type1
|
Type2
|
Type3
|
if condition
then statement1 statement2 .......... fi |
if condition
then statement1 statement2 .......... else statement3 fi |
"if condition1
then statement1 statement2 .......... elif condition2 then statement3 statement4 ........ elif condition3 then statement5 statement6 ........ fi |
To run simple test
|
If you wish to specify an alternate action when the condition fails
|
it is possible to test for another condition if the first "if" fails. Note that any number of elifs can be added.
|
#!/bin/bash
X=3
Y=4
empty_string=""
if [ $X -lt $Y ] # is $X less than $Y ?
then
echo "\$X=${X}, which is smaller than \$Y=${Y}"
fi
if [ -n "$empty_string" ]; then
echo "empty string is non_empty"
fi
if [ -e "${HOME}/.surya" ]; then # test to see if ~/.surya exists
echo "you have a .surya file"
if [ -L "${HOME}/.surya" ]; then # is it a symlink ?
echo "it's a symbolic link
elif [ -f "${HOME}/.surya" ]; then # is it a regular file ?
echo "it's a regular file"
fi
else
echo "you have no .surya file"
fi
| operator | produces true if... | number of operands |
| -n | operand non zero length | 1 |
| -z | operand has zero length | 1 |
| -d | there exists a directory whose name is operand | 1 |
| -f | there exists a file whose name is operand | 1 |
| -eq | the operands are integers and they are equal | 2 |
| -neq | the opposite of -eq | 2 |
| = | the operands are equal (as strings) | 2 |
| != | opposite of = | 2 |
| -lt | operand1 is strictly less than operand2 (both operands should be integers) | 2 |
| -gt | operand1 is strictly greater than operand2 (both operands should be integers) | 2 |
| -ge | operand1 is greater than or equal to operand2 (both operands should be integers) | 2 |
| -le | operand1 is less than or equal to operand2 (both operands should be integers) | 2 |
#!/bin/bash for X in red green blue do echo $X doneThe for loop iterates the loop over the space seperated items. Note that if some of the items have embedded spaces, you need to protect them with quotes. Here's an example:
#!/bin/bash colour1="red" colour2="light blue" colour3="dark green" for X in "$colour1" $colour2" $colour3" do echo $X doneCan you guess what would happen if we left out the quotes in the for statement ? This indicates that variable names should be protected with quotes unless you are pretty sure that they do not contain any spaces.
#!/bin/bash X=0 while [ $X -le 20 ] do echo $X X=$((X+1)) doneThis raises a natural question: why doesn't bash allow the C like for loops
function-name ( )
{
command1
command2
.....
...
commandN
return
}
Where function-name is name of you function, that executes series of commands. A return statement will terminate the function.
Example:#!/bin/bash files="$(ls)" web_files=`ls public_html` echo "$files" # we need the quotes to preserve embedded newlines in $files echo "$web_files" # we need the quotes to preserve newlines X=`expr 3 \* 2 + 4` # expr evaluate arithmatic expressions. man expr for details. echo "$X"The advantage of the $() substitution method is almost self evident: it is very easy to nest. It is supported by most of the bourne shell varients (the POSIX shell or better is OK). However, the backtick substitution is slightly more readable, and is supported by even the most basic shells (any #!/bin/sh version is just fine)
The command to collect GPFS Snap is "gpfs,snap" , this is very generic but very helpful.
# gpfs.snap
Note: The purpose of above command is to collect the snap on one node in the cluster,preferably the problematic one.
If the cluster is experiencing problems as a whole use -a flag
# gpfs.snap -a
Note1: -a flag only recommended for smaller clusters as it collects the logs for all of the nodes in the cluster.
Note2: -d option can specify the Output Directory but the default is
==> Another recommendation is collect an mmfsadm dump waiters
/usr/lpp/mmfs/bin/mmfsadm dump waiters > gpfs.waiters
/usr/lpp/mmfs/bin/mmfsadm dump all > gpfs.dump.all
/usr/lpp/mmfs/bin/mmfsadm dump kthreads > gpfs.dump.kthreads
==> Another file you need to check is log file
This information will greatly assist development in reviewing performance or problematic issues in GPFS.
