others-How to show full path or current working directory of a process in linux

1. Purpose

In this post, I would demo how to show the full running path or current working directory of a process in linux. Before start, we should know the definition of the phrase working directory:

In computing, the working directory of a process is a directory of a hierarchical file system, if any, dynamically associated with each process. It is sometimes called the current working directory (CWD), e.g. the BSD getcwd(3) function, or just current directory.

2. The problem and solutions

2.1 The problem

When we use ps -ef or top command to show processes in the linux system, we can only see the command name instead of the full path of the command, just as follows:

[root@genuine-post-2 ~]# ps -ef|grep java
root     24572     1  0 Oct11 ?        01:47:52 java -Xmx500m -Xms256m -cp ./libs/*:. com.bswen.WebApplication

We can only see the java process is running, but where does it run? e.g. We want to know which directory the java process is running in.

2.2 The solution #1

We can use the following command to print the working directory of the process:

pwdx <PID>

For example, our process’s PID is 24572, so we can check the working directory of the process as follows:

[root@genuine-post-2 ~]# pwdx 24572
24572: /opt/tweb

How does it work?

The pwdx command reports the current working directory of a process or processes.

When Linux starts a process, the system will create a folder named PID under the /proc directory, just as follows:

[root@genuine-post-2 ~]# ls /proc/24572
attr        cmdline          environ  io         mem         ns             pagemap      schedstat  stat     timers
autogroup   comm             exe      limits     mountinfo   numa_maps      personality  sessionid  statm    timerslack_ns
auxv        coredump_filter  fd       loginuid   mounts      oom_adj        projid_map   setgroups  status   uid_map
cgroup      cpuset           fdinfo   map_files  mountstats  oom_score      root         smaps      syscall  wchan
clear_refs  cwd              gid_map  maps       net         oom_score_adj  sched        stack      task
[root@genuine-post-2 ~]#

Here are some important file/subdirectories in the /proc/<PID> directory:

• The cwd symbolic link is the process running directory;

• The exe symbolic link is the absolute path of the execution program;
• The cmdline is the command line command entered when the program is running;
• The environ records the environment variables when the process is running;
• The fd directory is a symbolic link of files opened or used by the process.

2.3 The solution #2

Just as the above explanations, we can just use ls -l to print the absolute path of the process:

ll /proc/<PID>/exe

2.4 The solution #3

And we can also use the lsof -p command to print the current working directory of the process:

lsof -p <PID> | grep cwd

For example:

[root@genuine-post-2 ~]# lsof -p 24572|grep cwd
java    24572 root  cwd    DIR                8,2     4096   274362 /opt/tweb
[root@genuine-post-2 ~]#

What is lsof?

lsof command stands for List Of Open File. This command provides a list of files that are opened. Basically, it gives the information to find out the files which are opened by which process

What does lsof -pdo?

List all open files that are opened by a particular process: Each file is associated with some process ID. There can be many files that are opened by a particular process. By using lsof -p process ID, files opened by a particular process can be checked.

We can see the result of lsof -p 24572 as follows:

[root@genuine-post-2 ~]# lsof -p 24572
COMMAND   PID USER   FD   TYPE             DEVICE SIZE/OFF     NODE NAME
java    24572 root  cwd    DIR                8,2     4096   274362 /opt/tweb

3. Summary

In this post, I demonstrated how to print the current working directory of a process in linux system, the key point is understand where the linux system store the working directory information, then we can use pwdx or lsof commands to show it. That’s it, thanks for your reading.