1、linux下jps command not found

hadoop启动，使用命令jps，可是却提示找不到命令，

hadoop执行jps 报
jps -bash: jps: command not found

这条命令是在jdk下的bin目录下的一个可执行文件，我查看了一下我的jdk目录，发现有jps可执行文件，但是只是没有放在环境变量里面而已，环境变量可以通过etho $PATH命令查看。

所以就要自己加上去，以root身份vi /etc/profile，然后在下面加一行export PATH="usr/java/jdk160_05/bin:$PATH",其中橘色的部分是你把jdk安装在哪的路径和jdk文件夹名称。保存退出。

然后source /etc/profile就可以，没报错就说明是成功了，再执行jps就看到了。

2、配置环境变量错误，导致输入命令报错

ls -bash: ls: command not found

解决方案：
 export PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

重新配置/etc/profile

3、hadoop集群搭建问题Permission denied

[grid@HD1 bin]$ start-all.sh
Warning: $HADOOP_HOME is deprecated.

starting namenode, logging to /opt/hadoop-1.2.0/libexec/../logs/hadoop-grid-namenode-HD1.out
/opt/hadoop-1.2.0/bin/hadoop-daemon.sh: line 138: /tmp/hadoop-grid-namenode.pid: Permission denied
192.168.100.37: starting datanode, logging to /opt/hadoop-1.2.0/libexec/../logs/hadoop-grid-datanode-HD3.out
192.168.100.36: starting datanode, logging to /opt/hadoop-1.2.0/libexec/../logs/hadoop-grid-datanode-HD2.out
192.168.100.36: /opt/hadoop-1.2.0/bin/hadoop-daemon.sh: line 138: /tmp/hadoop-grid-datanode.pid: Permission denied
192.168.100.35: starting secondarynamenode, logging to /opt/hadoop-1.2.0/libexec/../logs/hadoop-grid-secondarynamenode-HD1.out
192.168.100.35: /opt/hadoop-1.2.0/bin/hadoop-daemon.sh: line 138: /tmp/hadoop-grid-secondarynamenode.pid: Permission denied
starting jobtracker, logging to /opt/hadoop-1.2.0/libexec/../logs/hadoop-grid-jobtracker-HD1.out
/opt/hadoop-1.2.0/bin/hadoop-daemon.sh: line 138: /tmp/hadoop-grid-jobtracker.pid: Permission denied
192.168.100.36: starting tasktracker, logging to /opt/hadoop-1.2.0/libexec/../logs/hadoop-grid-tasktracker-HD2.out
192.168.100.36: /opt/hadoop-1.2.0/bin/hadoop-daemon.sh: line 138: /tmp/hadoop-grid-tasktracker.pid: Permission denied
192.168.100.37: starting tasktracker, logging to /opt/hadoop-1.2.0/libexec/../logs/hadoop-grid-tasktracker-HD3.ou
解决办法：
1.)在hadoop-config中修改hadoop-env.sh，添加：export HADOOP_PID_DIR=$HADOOP_HOME/run/tmp。改变pid的路径。3台机子一块改。
2.)在/etc中修改profile，添加：export HADOOP_PID_DIR=$HADOOP_HOME/run/tmp，同样，改3台机子。