Sed Command Hangs During MySQL MHA Installation Due to Charset Mismatch and Comment Formatting

The author, responsible for Oracle, MySQL, MongoDB and Redis maintenance, reports that running sed -i "s/.*vip.*ping valid.*/#&/g" mha_install.sh on a MySQL server installation script hangs, with the sed process consuming 100% CPU.

Using top and pstack , the stack trace shows the process stuck in the gconv() function, which performs character‑set conversion. The script file is UTF‑8, while the current session locale is zh_CN.gbk , causing the conversion to fail.

file -i mha_install.sh
mha_install.sh: text/x-shellscript; charset=utf-8
locale
LANG=zh_CN.gbk
...

Setting LANG=en_US disables the conversion and the sed command returns instantly.

export LANG=en_US
sed -i "s/.*vip.*ping valid.*/#&/g" mha_install.sh

To locate the problematic line, a binary search pinpoints line 325, which contains a comment without a space before Chinese characters ( #生成密钥对 ). This format triggers the bug in older sed versions.

head -n 325 mha_install.sh|tail -1
#生成密钥对

Testing with a file that has a space after the comment symbol ( # 生成密钥对 ) shows sed works correctly, confirming the issue.

cat fxtest.txt
# 生成密钥对
#生成密钥对
head -n 1 fxtest.txt |sed -n '1,$p'
# 生成密钥对

The problem appears on CentOS 6 with GNU sed 4.2.1, while CentOS 7 ships sed 4.2.2, which does not exhibit the bug. Replacing the older sed binary with the newer version resolves the hang.

sed --version
GNU sed 4.2.1
# on CentOS 7
sed --version
sed (GNU sed) 4.2.2
# copy newer sed and run
chmod +x sed && head -n 2 fxtest.txt |./sed -n '1,$p'
# 生成密钥对
#生成密钥对

Summary

Always insert a space between comment symbols and Chinese characters in shell scripts.

Older versions of tools like sed may contain charset‑related bugs; upgrading or adjusting the environment can eliminate such issues.