将输出重定向到文件时出现问题

Question

下面是我的脚本，只要内存低于500 MB就会检查并发送电子邮件，如果我手动运行它会完美运行.. 如果我通过cron安排它 - 下面一行的输出没有被捕获到输出文件。

ps -A -opid | sudo xargs -n1 -I{} /bin/bash -c 'echo {} $(ls /proc/{}/fd | wc -l);' >> /home/utilization.txt

代码

#!/bin/bash

ip=`ifconfig | grep -oP '(?<=inet addr:)\d+\.\d+\.\d+\d+'`

free=$(free -mt | grep Total | awk '{print $4}')

if [[ "$free" -le 500 ]]; then
    ps -eo pid,ppid,cmd,%mem,%cpu --sort=-%mem | head > /home/utilization.txt

   echo -e "******************************************************************" >> /home/utilization.txt
   echo -e "******************************************************************\n" >> /home/utilization.txt
   echo -e  "Current active Process and open files\n" >> /home/utilization.txt

   ps -A -opid | sudo xargs -n1 -I{} /bin/bash -c 'echo {} $(ls /proc/{}/fd | wc -l);' >> /home/utilization.txt

   file=/home/utilization.txt

   echo -e "memory is running low on $ip Available memory: $free MB" | mailx -a "$file" -s "Check memory Status" myemail@gmail.com
fi
exit 0

如果通过cron运行输出文件

  PID  PPID CMD                         %MEM %CPU
    1     0 /sbin/init                   0.0  0.0
    2     0 [kthreadd]                   0.0  0.0
    3     2 [migration/0]                0.0  0.0
    4     2 [ksoftirqd/0]                0.0  0.0
    5     2 [stopper/0]                  0.0  0.0
    6     2 [watchdog/0]                 0.0  0.0
    7     2 [migration/1]                0.0  0.0
    8     2 [stopper/1]                  0.0  0.0
    9     2 [ksoftirqd/1]                0.0  0.0
******************************************************************
******************************************************************

Current active Process and open files

手动运行时输出文件

PID  PPID CMD                         %MEM %CPU
    1     0 /sbin/init                   0.0  0.0
    2     0 [kthreadd]                   0.0  0.0
    3     2 [migration/0]                0.0  0.0
    4     2 [ksoftirqd/0]                0.0  0.0
    5     2 [stopper/0]                  0.0  0.0
    6     2 [watchdog/0]                 0.0  0.0
    7     2 [migration/1]                0.0  0.0
    8     2 [stopper/1]                  0.0  0.0
    9     2 [ksoftirqd/1]                0.0  0.0
******************************************************************
******************************************************************

Current active Process; their PIDs and the open files

PID 0
1 8
2 0
3 0
4 0
5 0
6 0
7 0
8 0
9 0
10 0
.....
....

我不确定我哪里出错了。