Scripting Experience

Yao Yao on September 17, 2015

Backup My Ubuntu


最近在写一个脚本,在 VirtualBox 5.0.4 + Ubuntu 14.04 上通过 samba mount 到 MacMini 上做备份,然后通过 gmail 发邮件通知。

1. Mounting

1.1 VM Config and Network Accessibility

Make sure that VM network is configured to use NAT (on eth0).

假设目标 ip 是 我们可以做一下连接检测:

telnet 445 # 445 is the port number. 23 by default

1.2 Mounting to MacMini

目前 mount -t smbfs 是 deprecated,需要使用 mount -t cifs 或者直接使用 mount.cifs。前提是你需要安装 cifs.utils:

sudo apt-get install cifs.utils

samba 和 cifs 的关系是:cifs 是协议,samba 是 cifs 的一个实现。

然后其他的参数,因为是 Mac,所以要指定为 nounix,sec=ntlmssp,具体可以 google “ubuntu samba mount mac” 查询。我最终的命令是:

sudo mount.cifs // /mnt -o username=bar,password='baz',nounix,sec=ntlmssp,noperm,rw

一般 password 是不用加引号的,只有在有特殊字符需要转义的情况下才需要加上引号。

也可以把 username 和 password 写到一个配置文件里(配置文件的密码里即使有特殊字符也可以不用加引号):

## ~/Documents/cifs_credentials
sudo mount.cifs // /mnt -o credentials=~/Documents/cifs_credentials,nounix,sec=ntlmssp,noperm,rw

1.3 Error Log

tail -100 /var/log/syslog

1.4 mount & /etc/fstab

If you mount.cifs without sudo, you’ll probably get the error log like:

mount.cifs: permission denied: no match for /mnt found in /etc/fstab

You need to add an entry in /etc/fstab like:

# // /mnt cifs user,uid=1000,rw,suid,username=xxx,password=xxx,noauto 0 0

in which, uid=1000 is fixed and can be obtained by command id <usename>, and noauto option means you wish to manually mount it instead of getting mounted by boot automatically. For more details, see How to mount remote Windows shares.

However, if put the script under sudo crontab -e, you don’t have to bother with /etc/fstab.

1.5 mount error(127): Key has expired

If you run mount.cifs inside a cron task, you will probably get this weird error. Actually it has nothing to do with the key nor the expiration.

According to weird cron job issue, crontab could not locate your commands in PATH under some conditions, so a easy solution is to use the full path of the command, like /sbin/mount.cifs for mount.cifs, in you script.

You can obtain the full paths by whereis <command>.

2. Sending Emails

2.1 Basis

首先装一个 SSMTP,参照 How to Send Email via SMTP Server from Linux Command Line (with SSMTP)Configuring send emails using GMail Account in CentOS 6 with SSMTP。需要注意的是,Ubuntu 的 TLS_CA_File 不是 /etc/pki/tls/certs/ca-bundle.crt 而是 /etc/ssl/certs/ca-certificates.crt

sudo apt-get install ssmtp
## /etc/ssmtp/ssmtp.conf

# The person who gets all mail for userids < 1000
# Make this empty to disable rewriting.

# The place where the mail goes. The actual machine name is required no
# MX records are consulted. Commonly mailhosts are named

# Where will the mail seem to come from?

# The full hostname

# Are users allowed to set their own From: address?
# YES - Allow the user to specify their own From: address
# NO - Use the system generated From: address

安装完 mailutils 我们就可以发信啦:

sudo apt-get install mailutils

echo "BODY" | mail -s "SUBJECT"

2.2 Sending to multiple address

用 shell 的 array 就好了:

mailtoaddr=("" "")

for addr in "${mailtoaddr[@]}"; do
	echo "System ${myhostname} backup done on $(date +'%r, %m/%d/%Y')" | mail -s "Backup Done!" ${addr}

2.3 Changing the From address

因为 bot@gmail 是用我的 first name 和 last name 注册的,所以收信方看到的都是我的 first name。想让收信方看到不同的名字(比如 “bot”),在 Gmail 里设置是不起作用的(Settings -> Accounts and Import -> Send mail as),需要在命令行里指定一个新的 Header:

sudo apt-get install mailutils

echo "BODY" | mail -s "SUBJECT" a "From: bot <>"

-> ~~~~~~~~~~ 2016/01/04 P.S. Start ~~~~~~~~~~ <-

Today I met a problem when testing echo "BODY" | mail -s "SUBJECT"

mail: cannot send message: Process exited with a non-zero status

I checked the log, commanding tail /var/log/mail.err:

Jan  4 16:38:12 <hostname> sSMTP[23511]: Authorization failed (534 5.7.14 blahblahblah - gsmtp)

As how to fix “send-mail: Authorization failed 534 5.7.14” suggested, the solution is:

Log into your google email account and then go to this link: and set “Access for less secure apps” to ON.

-> ~~~~~~~~~~ 2016/01/04 P.S. End ~~~~~~~~~~ <-

3. Encrytion

Easy. Use openssl.

# encrypt
openssl enc -aes-256-cbc -salt -in file.txt -out file.txt.enc -k PASS

# decrypt
openssl enc -aes-256-cbc -d -in file.txt.enc -out file.txt -k PASS

Use -k option if you don’t want to input password interactively.

For more ciphers, just openssl --help.

4. Disable cron’s email notification

When executing commands, any output is mailed to the owner of the crontab (or to the user specified in the MAILTO environment variable in the crontab, if such exists).

So, we need to ‘silent’ our cron task. One way is to use the “quite mode” if there is an option for the command; the second one is to redirect the output, e.g. to a log file.

A typical configuration would look like:

* * * * * >> /var/log/myjob.log 2>&1

2>&1 means to combine stdout and stderr into the stdout stream, so you’ll see both stdout and stderr in your log file.

5. Shell Techniques

5.1 Exit code of the last command

exit code 我们可以用 echo $? 获取,为 0 时表示 last command 执行成功;非 0 表示出了问题。


if [ $? -eq 0 ]
    echo "it worked"
    echo "it failed"


if my_command
    echo "it worked"
    echo "it failed"

5.2 A command that always fails

false 命令必定会失败,所以可以用来测试命令出错的情况。

5.3 For every element in array

mail_to_addr=('' 'janedoe@baz.qux')

for addr in "${mail_to_addr[@]}"; do
	echo ${addr}

5.4 You can output an array as is

E.g. If you want to make up a command like tar -cpzf test.tar.gz --one-file-system /foo /bar, you can write:

tar_targets=('/foo' '/bar')

tar -cpzf test.tar.gz --one-file-system ${tar_targets[@]}

5.5 Add prefix or suffix to every element of an array

array=( "${array[@]/%/_suffix}" )

array=( "${array[@]/#/prefix_}" )

A typical use is to generate multiple --exclude parameters for tar:

tar_exclude=('/foo' '/bar')
tar_exclude=( "${tar_exclude[@]/#/--exclude=}" )

tar -cpzf test.tar.gz --one-file-system ${tar_targets[@]} ${tar_exclude[@]}

The script above would generate --exclude=/foo --exclude=/bar.

MySQL Query


1. mysql -A

From “The MySQL Bible” by Steve Suehring:

Speeding startup of the CLI

When the CLI starts, it reads in table information to allow for completion, which can sometimes slow the startup. To turn off this default and get a quicker CLI startup, use the -A or --no-auto-rehash switch. Adding --no-auto-rehash to the MySQL configuration file under the [mysql] section makes this quicker startup permanent.

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